The short answer is yes, it does matter.
Kids need to, at a minimum, be getting enough calories to adequately
grow, and they need to be getting that in some balance of
carbohydrates, fats, and protein. That's not to mention the variety
of nutritional deficiencies that can arise from lack of specific
vitamins, minerals, or other nutrients. Iron deficiency (which will
usually first manifest as anemia) is one of the more common ones seen
in kids, but there are a host of others. As a whole, other vitamin
deficiencies are rare in the US, where we fortify/supplement our
breads, cereals, orange juice, salt, etc. There are whole textbooks
on pediatric nutrition, so I won't even attempt to cover all of this.
The American Academy of Pediatrics has lots of great resources on the
topic, which you can access here:
I'm guessing your question, however, is more of the "my 2 year old
refuses to eat peas" type. Some degree of food pickiness is common in
most toddlers. My general advice is:
1. Don't make it a fight. If you do, it becomes a
control/independence issue, and forcing a kid to eat a particular food
is impossible. Be reasonable, encourage you child to eat it, and
continue to offer it with meals. You'll likely be able to talk them
into eating just one spoonful of peas, for example, and next time you
can work on two spoonfuls. With a little persistence, they'll get
used to the flavor & texture, or just forget that they hated peas
2. Role model healthy eating habits. If the rest of the family
doesn't drink milk, it's hard to convice a toddler to drink it. Same
goes with fruits, vegitables, and other healthy foods. Conversely, if
everybody at home eats crap (chips, cookies, candie, soda) you can't
expect your child will want to eat his carrots.
3. Make sure your pediatrician is involved, to make sure he's getting
a balanced diet. Refusing milk isn't a big deal, as long as there's
another source of calcium and protein (cheese, yogurt, etc). Same
with other vitamins & nutrients.
4. Don't give the child junk food (candy, soda, juice) if they're not
eating a balanced diet. Potato chips do not count as a vegitable,
fruit juice doesn't count as a fruit, candy doesn't count as a
carbohydrate, etc. You get the picture.
Good luck, and have your child's pediatrician give you more specific
advice. This information, obviously, is not a substitute for good