Infancy and childhood: what changes and what helps your daughter grow

What changes in infancy and childhood?

In infancy and childhood, a girl's body is quietly building bone, brain, iron stores, immune defenses and teeth, long before anything looks different from the outside. If you are wondering whether your daughter is on track, it helps to know that this slow, steady building is normal, and that a few simple habits support nearly all of it.

Bone. Bone is built throughout childhood, ready for the big gains of puberty. The evidence shows that active children build stronger bones, so running, climbing and playground games are doing real structural work, even when they look like plain fun. None of it needs to be organized, because ordinary active days count.

Brain and development. The brain grows fastest in the first 2 to 3 years. Talking, reading and play drive language and social skills in this window, which is reassuring for any family with a busy week: chatting through the grocery run, a picture book at bedtime and time on the floor together all count, and none of it has to look like a lesson.

Iron. A baby is born with a store of iron, and that store runs low by about 6 months, which is why first foods matter. Toddlers who drink a lot of cow's milk are also at risk of iron deficiency, because milk can fill a small stomach before iron-rich food does.

Immune system. Babies get some protection from their mother, and it fades over the first months. Keeping up with vaccinations on schedule gives steady cover as that protection lessens, and breastfeeding adds to it if it works for your family. In the UK the schedule is set out by UKHSA, and in the US by your pediatrician's well-child visits. If breastfeeding isn't possible or isn't what suits you, the vaccination schedule still does the main work.

Teeth. Tooth decay is one of the most common chronic conditions of childhood in the US, and in the UK it is the most common reason young children need hospital treatment. Baby teeth count, and they are worth looking after from the first one that appears. A dentist can show you what suits your child's age.

Early signs of puberty. Childhood ends gradually. Breast development usually starts between 8 and 13, and that whole range is normal. Signs before 8 are worth having checked by a pediatrician (a GP in the UK).

What helps a girl grow strong in infancy and childhood?

Four things do most of the work: vitamin D, well-timed first foods, daily movement and enough sleep. None of them needs to be perfect. A good place to start is whichever one feels easiest in your home this month.

Vitamin D. The American Academy of Pediatrics advises a daily dose for breastfed and partly breastfed babies from birth, and the UK's 10 µg matches it. It is a small dose that many parents fold into an existing routine, such as the first feed of the day.

First foods. Starting solids, called weaning in the UK, happens at about 6 months. The evidence supports including iron-rich foods from the beginning, such as meat or iron-fortified cereal, and offering common allergens early, not late. The LEAP trial, published in the New England Journal of Medicine in 2015, is the study behind early peanut introduction.

Milk for toddlers. Keeping to 2 to 3 cups (16 to 24 oz) a day leaves appetite for the iron-rich foods toddlers need.

Active play. From age 5, a sensible target is 60 minutes or more a day. It can come in pieces: the walk to school, recess, a game in the yard. Under-5s need about 3 hours of movement spread across the day, and crawling, climbing and dancing in the kitchen all add up.

Sleep. Children sit at different points along the ranges, so there is room for your child's own pattern, and a bedtime routine that suits your household matters more than hitting a precise hour.

Next steps

If you would like a place to start, pick one of the four numbers above and see how it sits with your family's days. Keep the red flags list somewhere handy, and bring any question, large or small, to your pediatrician, or to your health visitor or GP in the UK. Every child grows on her own timetable and every household runs differently, so take what fits yours and leave the rest: not one size fits all.