R.F.
If you are having the party in a place with a yard or outdoor area get them each cans of silly string (try a dollar store) and call it spiderweb and let them "get" each other with it. You could even break them into spidermen and black spidermen like the latest movie and get them masks or let them make them so they who is on which team.
Get a spiderman pinata and fill it with leftover trick or treat candy. The pinatas now come with strings to pull so you don't have to hit it with anything so they are good for inside parties and younger kids.
If you really want to get the babies something, which you don't have to, you could get them each a small stuffed animal or toy thats age appropriate.