This article is from the Children Allergies and Asthma FAQ, by Eileen Kupstas Soo firstname.lastname@example.org with numerous contributions by others.
Allergies can show themselves in a number of ways -- runny noses, ear
infections, digestive disorders, irritability, hyper- and hypo-
activity, and such. Adults are often more sensitive to "not feeling
right" than children are, so look for indicators such as changes in
behavior or chronic/repeated sickness the corelates to exposure to
various substances (foods, air-borne particles, chemicals, etc.).
Recurrent stomach aches, never-ending ear infections, or changes in
bowel habits may indicate that an allergy is present. In infants,
colic, formula intolerance, frequent spitting up, and low-grade fevers
can be signs of allergies. Note that allergic reactions will not occur
on first exposure to the allergen; they require that initial
"priming." Some may occur on second exposure, while others may take
repeated exposure to develop.
For infants, breastmilk is the safest food, in terms of allergies.
Some children are allergic to or intolerant of cow's milk, soy
formulas, and such. The best advice is to experiment until you find
what works for your child. (Some mothers report that the mother's
consumption of cow's milk will cause a reaction in a breastfed
child; this has been confirmed by medical experts, so you may need
to check this if your child is breastfed. References to this and
other infant issues are given at the end of section 8. )
When a child is born, the intestinal track is not fully developed.
Some foods may cause a reaction in babies that will be outgrown as
the child matures. The safest course is to introduce new foods one
at a time over an extended period (say, one food per week) and see if
the child has an allergic reaction. Postponing the introduction of
common allergens (wheat, cow's milk, corn, eggs) and favoring the
introduction of almost-always-safe foods (rice, apples, bananas) is
one sensible approach.
For older children, allergies can have any of the symptoms above. If a
child is extremely reluctant to eat a particular food, there may be an
allergy problem that shows up as a stomach ache (common in milk
intolerance) or other non-visible way. On the other hand, while most
children will avoid foods which make them really sick, some may NOT
make the connections when the allergy is mild. So parents need to
listen to the child and use common sense and detective abilities to
help determine the problem.
Children may outgrow some allergies, or at least become less sensitive
to some allergens. Parents may want to retry foods after a long
period. NOTE: if the allergy is a severe one, do NOT retest the
food on your own! Do this only under the supervision of your doctor!
For less severe allergies, you can first test the allergen by rubbing
a bit on the child's wrist (inside) and see if a skin reaction occurs. If
no reaction occurs, let the child try a very small amount of the
food. Again, if no reaction occurs, let the child try a slightly
larger amount. The child may never be able to eat a lot of the
food but may be able to tolerate small amounts after a "rest"
period away from the allergen.