I am a preschool teacher so I have a pretty good idea about activities for this age group. First of all no child in this age range can resist a balloon (not helium filled but just blown up with a short string). The one year olds should be ok with the balloons as long as you don't have any popped balloon pieces lying around. The next thing you need to do is get a CD called "Greg and Steve Kids in Motion" (available online or at most music stores that has kids music). They have a freeze dance song, where the children can dance around (with their balloon) until the music stops and says freeze. The 3-4 yr olds will love it and the younger ones will have fun copying the older kids even if they don't really understand the directions. There are several other fun songs on the CD too; "Animal Action" where the kids dance around and imitate the zoo animal specified in the song, etc. Kids this age also love a pinata. They make ones that have streamers you can pull to open a trap door, instead of using a bat. You can fill the pinata with stickers and tatoos or other small age appropriate prizes instead of candy. Also, you can add streamers (just tape some extra pieces on) to insure everyone gets a turn. To preserve your sanity, I wouldn't make the party much more than an hour and a half. That gives you about 45 minutes of activities and 45 minutes for cake and things. I would also suggest that you save presents for after the party guests leave. Kids this age have lots of trouble watching another child open presents when they don't get any. It will save a lot of tantrums ;) Have fun, good luck, hope this helps!!