Some children are picky eaters from the time they start solid food. Others children eat anything put in front of them and are a delight to feed. I had one of each! When parents worry that a child may starve if they don't cater to their every whim, trouble lies ahead. Unless a child has an eating disorder, celiac disease, or serious allergies, they are not going to starve if food is available. My advice to parents has always been to put tasty, colorful food in small portions in front of the picky eater and then if the meal is not eaten to get the child down from the table. After a few missed meals, kids will begin to eat what is put before them.
One problem that often arises is when parents let a child fill up on milk or eat a lot of snacks between meals. Milk should just be available at mealtime and no snack, except perhaps for apple juice, given between meals. When a parent tells me a child is having trouble with meals, I have always asked them to keep a three day list of everything the child eats and mail it to me. I have seen some astounding lists. One little boy was a very picky eater and his pediatrician thought his lack of strength was due to a muscle weakness. He was a sickly looking little boy, but on listening to the single mother's very busy schedule, I suspected some changes needed to be made. The family lived on fast food. The three days list of food was astounding. I suggested the mother do shopping and meal planning on the weekends and get the children involved in planning the meals. After two to three weeks, the little boy was eating much better and the whole family felt better. I cured the suspected muscle disease by listening to what what going on in the family. We do reflect what we eat.