How does nutrition underpin developmental milestones in toddlers?

Toddlerhood is a crucial stage in child development. Between birth and three years, the height of a toddler doubles, and their weight can increase three or fourfold (WHO 2020). In addition, by the age of three, the brain reaches 80% of its adult size (Huelke, 1998). However, this stage often does not receive as much attention from caregivers and healthcare professionals as the first months of life.

During toddlerhood, a child’s cognitive skills, social-emotional skills, and sensory-motor skills are all developing rapidly (Cusick & Georgieff, 2016). Directing attention to this stage of life can support the normal development of these skills, setting the child up for optimal development and a greater chance of success throughout their life.

Advancements in these interconnected skill areas are underpinned by rapid functional and structural maturation of the brain, including the creation and strengthening of neural networks. This process is influenced by environmental factors, as development occurs alongside changing nutritional needs. Nutrition impacts the development of sensory-motor, cognitive and social-emotional skills, providing the building blocks for cell proliferation, DNA synthesis, and neurotransmitter and hormone metabolism, amongst other roles. In early life and toddlerhood, organs such as the brain develop rapidly compared to the rest of the body, and this makes them particularly vulnerable to dietary deficiencies.

Understanding healthy development and developmental milestones, and their links with nutrition, is important for health care professionals.

Lifelong diet quality and dietary patterns are often established during toddlerhood, when a child is building foundational food preferences and healthy eating behaviours, and this stage requires adequate dietary intake (Beckerman et al, 2017). Inadequate intake of the main macronutrients – fats, proteins, fibres and carbohydrates – as well as micronutrients, such as key vitamins and minerals, can have long-lasting effects on child development, as well as a child’s health and well-being later in life (Agosti et al, 2017).

Developmental milestones
The first years of life are characterised by the achievement of different developmental milestones. Milestones can be defined as physical skills or behaviours exhibited by children that fall within three domains: sensory-motor, social-emotional, and language-cognitive domains. These milestones follow a predictable course in infants and children, as each developmental stage builds upon the skills achieved in previous stages. Understanding healthy development and developmental milestones, and their links with nutrition, is important for health care professionals to be able to recognise developmental delays and optimise healthy development.

At around 12 months, a child begins to walk as a consequence of the developing motor system. Walking requires coordination of physical and neurological development. Protein, calcium, magnesium and vitamin D are vital in supporting this development, helping to build normal bones and muscles (EFSA, 2008, 2009), which enable a toddler to support their own weight. Once able to explore the environment by themselves, many new possibilities are open to the toddler, and this has subsequent effects on other learning domains, such as social-emotional and cognitive skills. It is around the age of one year that toddlers engage even more actively with their environment: pointing at objects, returning hugs and matching objects to the corresponding shapes on a board.

Other important milestones are observed at two years of age. Although a fraction of their adult age, a two-and-a-half-year-old has already developed a bone structure that is 50% of their adult skeleton height (Colson and Dworkin, 1997). Complex motor-skills, such as kicking a ball and walking up and down stairs with support, have been mastered. At this age, we continue to see the toddler’s emotional and social skills develop, supported by the maturation of an area of the brain called the limbic system. This means toddlers can better express personality traits, as well as their thoughts and needs. Whilst toddlers at this stage show emotions, they often do not fully know how to control them, as demonstrated by temper tantrums during the infamous ‘terrible twos’! This is accompanied by progress in cognitive ability; toddlers are now able to follow simple commands and recognise familiar objects.

To support development of a two-year-old’s nervous system, a range of B vitamins, including vitamin B3 (niacin), are required to support the nervous system (EFSA, 2009b & EFSA, 2010) and to help social skills develop effectively (Kennedy, 2016). Some B vitamins like Vitamins B1, B6 and B12 also contribute to psychological function, a key factor when a toddler is experiencing so many new challenges and experiences on a daily basis (EFSA, 2010 & 2010b, 2009c).

Next, three years of age represents a period of high sensitivity for ensuring important cognitive milestones are reached, coinciding with continuous maturation of the prefrontal cortex in the brain. At this stage, the child starts to become more independent. Cognitive development is supported by iron (EFSA, 2013) and zinc (EFSA, 2009d), and vitamin C also plays an important role in psychological functions (Huskisson et al, 2007). In terms of motor skills, toddlers are now able to move more efficiently; for example, they can stand on one leg and undo buttons. They are also able to understand more about the world around them and become more curious and imaginative, which boosts their social-emotional skills.

Nutritional deficiency is a global issue in both developing and developed countries.

These changes are linked to later developments, which can be supported by adequate iron and zinc intake. Iron intake can also be optimised through ingestion of vitamin C-containing foods alongside iron-rich foods. There is some evidence that iron deficiency anaemia in children can have long term impacts on cognitive function. Finally, good fats such as DHA and ALA can also contribute to effective brain development. These can be found in foods such as oily fish and fortified growing up milks (EFSA, 2014).

Choosing the right nutrition
In order to develop many of these skills, toddlers rely on exposure to other children and adults, alongside adequate nutrition and enabling environments. Development of the immune system is of crucial importance, as a child who is sick misses out on opportunities to play with other children, to attend nursery or school, and to experience new activities. Nutrients known to support the immune system include iron, zinc, selenium (EFSA, 2009d, 2009e & 2009f) and vitamins A, C and D (EFSA, 2009g, 2010c, 2013b). When breastfeeding is stopped, it is important to choose the most appropriate feeding option with which to continue. In this respect, caregivers and healthcare professionals can help parents provide adequate nutrition for optimal toddler development.

Growing up milks provide adequate milk options for non-breastfed toddlers including adapted protein levels, vitamins and minerals to complete their diet. This means that they are good options for meeting nutritional requirements, especially in areas of the world where nutritional deficiencies are common. Toddlers who consume growing up milks have been shown to have higher intakes of some key nutrients compared to toddlers who consumed other milks or non-dairy consumers (Mak et al, 2020). Some growing up milks also contain probiotics such as L. rhamnosus, which helps promote a healthy gut flora and a lower rate of absence from day care due to illness was observed in children receiving L. rhamnosus (Hatakka et al, 2001 & Hojsak et al, 2010).

Cows’ milk is not necessarily adapted to meet these high nutritional needs and does not contain sufficient iron or vitamin D to meet the needs of toddlers. Growing up formula may be beneficial to close the nutritional gap between inadequate intake from diet and recommended nutrient values. Other fortified foods may also help to bridge the gap: many foods, such as baby cereals, are already fortified with nutrients, including iron, calcium and some B vitamins.

Ensuring that toddlers receive adequate nutrition is key to helping them reach their full potential as they grow and progress through the different developmental stages during their first years of life. Improved understanding of toddlerhood means that we can better monitor a child’s development, identify any developmental delays, and intervene early if there are problems with development or nutrition.