Is it safe to give my 16 month old (who weighs 19lbs) children's Claritin instead of Benadryl (diphenhydramine) for allergies?

Not approved . 16 months is a young age and not many medications are approved for allergies. The best thing to do is to call pediatrician as each child is different in needs and peds knows the kid best.
Yes. Either is safe, just follow the dosing guidelines for the child. Claritin (loratadine) is in the non-sedating family, bendryl is in the sedating family.