Can you give a 14wk old kitten childrens Benadryl?

No, do not give your kitten Benadryl. It is called Children's Benadryl" not "Kitten/Cat Benadryl". If your kitten is ill, take him/her to see a vet. A child can easily be 75 times larger than a kitten. That would be the same as a child taking an entire bottle of "Aspirin" for a headache.Not a wise choice, it may be a deadly choice. Just pop over to see the vet , he/she will make your kitten well again.