S.K.
You can bring them to any local resale shop. They all take car seats that are in good condition and have no recalls. Then you can make a little money on them. You can also donate them to Goodwill or join your local Freecycle and offer them up to someone who may need them.
You can also call the SafeKids group and ask if there is anyway to donate them that way. Social workers may have a need as well.
I know that My Cousin's Closet resale shop in Gales Ferry donates to Karyn's Closet- which is an organization that collects clothing and gear for children in Foster Care. You could probably drop them there to be donated to that charity.
Good luck!