Every child is unique and grows up at her own pace. At age 3, some look more like they are 7, while other kids at age 6 may still look like toddlers. There is no right or wrong, but there are some general guidelines into which the majority tend to fall.
According to the website PBS.org, most 3-year-olds move with more confidence than toddlers and are able to run, bike and climb. They are good with their fingers, are able to hold crayons without using the whole hand, and can put together simple puzzles. By the time they're approaching 7, they are more proficient in moving their bodies and are able to jump, roll and stand back up, and change directions while running, but they're still not great at kicking, catching, striking and throwing.
The educational website NCStateCollege.edu points out that the "average 3-year-old weighs 13.6kg. and from 3-6 years they grow on average two to three inches and gain 1.8-2.7kg." It also mentions that 3-year-old lose baby fat and their trunk and limbs grown longer, making them look more athletic and slender. Their heads, still big in relation to their bodies, start to look more proportionate as the years pass.
Boys and girls do not develop the same way. NCStateCollege.edu states that "boys' edge in height and weight continues until puberty, when girls surpass boys." It also says that young boys have more muscle mass pound for pound relative to young girls, who have more fatty tissue. This will make the young boys stronger than girls.
The British website Kidsdevelopment.co.uk claims, "Scientists say that superfoods can help your child's development." The site counts apples, oranges, kiwi fruit, eggs, onions and fish among the groceries that may help your child turn out the best he can be. Oranges, for example, are a good source for calcium, which helps promote strong bones in growing kids.
A child's appetite decreases as growth slows. Three- to 6-year-olds will eat less in proportion to their size than infants do because their growth is slowing down. A 3-year-old will only eat enough to feel satisfied while a 5-year-old will keep eating if he likes what is being served or is forced to "clean his plate". Keep in mind that child obesity rates are on the rise; extra food will not grow them taller, only wider.