Birthday-party Activities for 3- and 4-Year-olds

Just do a Google search for "games for 3-4 year olds."

for mid-october, you could have a simple fall craft like get each child a miniature pumpkin to decorate with washable markers and/or stick-on eyes, noses, and mouths. But like others have said, a few free-play activities (bubbles, homemade play doh, sidewalk chalk, etc.) will keep the kids entertained.
Also, since this will be before halloween - you could get some plain gift bags and let the kids decorate them to use as trick or treat bags

What is the theme? I just had a b-day party for my 3 yr old. It was dinosaur themed. So I had gotten a dino stamp set and a few ink pads. Also, at Michael"s or AC Moore, they have these foam pads and foam stickers that stick on the pads. They have EVERY theme you could want. I also had dino's for those. It was good because both activities offered boy and girl colors. The kids spent about 30 min doing the activities and had a great time. If you want more ideas- message me. I am pretty creative when it comes to crafts/ideas for the kiddo's. I'd be glad to help you brainstorm.

You can get a bouncer/jumper. Pin the tail on the donkey. Get a piniata. Or do a craft. Just some idea's I've done with my kids. Good luck. it sounds like fun.

Make sugar cookies and have them frost and decorate

Play freeze dance

Get a bunch of little toys (we did rubber ducks) and have a scavenger hunt

Blow up a ton of balloons and have them throw them around either inside or out.

Get an electric bubble blower and have an outside dance party

But mostly they'll just be happy to play with the "new" toys. Make sure that your kids are ready to share their stuff or put away whatever they "can't" share and it should be a good time!

I've had several of these and i found that kids just want to play. So have a few games like duck duck goose and musical chairs, but free play is great and spreading things out is good as it cuts down on the fighting over same stuff. i move my kids stuff into different areas so that the kids can be spread out.. my hubby & I blew up 150 balloons and had them all over the floors in my kids rooms. They love waking up to it and seeing it first thing and they all had a ball popping them all during the party. We make that a game and see how fast they all can get popped. I have my sister who always volunteers to clean up the mess and it really isn't very hard to do. she picks up the biggest pieces then vacuums the rest. I also take recycled tissue paper and when unwrapping the gifts, we throw out loads and loads of paper then everyone balls them up and we have a tissue paper ball fight while the gifts are being opened and that is a lot of fun too. hope this helps you.

I taught a 4 yr old preschool class and my kids loved musical chairs, dancing, duck duck goose...

If you could get 2 flat rubbermaid tubs, fill one with water, one with sand/rice, kids seem to like playing in them. If you can make different centers:babys, art(playdoh), dress up, water/sand area, bubble/music area (kids love BuBuLes... I think anything with art, food, and music would be a winner!

What about a decorate your own cookie/cupcake table?? You said there would be adults as well...

Have fun!