“What can you give a 3 year old for allergies?”

The first thing is to be sure that it is allergies. If thatt is indeed the case then it depends on whether the cause can be identified and avoided.
That being said, nasal steroid sprays, antihitaminics such as Claritin, Zyrtec and Allegra will be first line options. This is best done with supervision of your child's pediatrician.

That depends on what type of allergic problem. For noses children’s Claritin or Children’s Zyrtec can be used, check dosing instructions. Also, a nasal steroid spray like Nasonex can be used. For stuffiness, Singulair can also be used.

Thanks,

Dr. C