My 10 month olds eyelid is swollen and red under he is acting fine no fever what could it be?

Chalazon: Lois, It is probably a chalazon (like a pimple under the eyelid). These are treated with warm compresses 4-5 times a day. If it doesn't resolve, please take him to his doctor. Hope this helps!

Allergy/irritation: I would suggest a pediatric exam. Without a photo you may want to ask your peditrician about pediatric antihistamine.

Swollen/red eye: My big question is if it's just one eye or both? If just one eye, I'm much more concerned about an infection - whether a stye developing, a bug bite that is getting infected or reaction, or an infection called periorbital cellulitis, which can be very serious. If both eyes more likely allergy source. Cool compress area, try a dose of Benadryl, (diphenhydramine) but if ill in ANY WAY or FEVER, go to ER today.