This sounds like a cute idea. What is the age range of the kids, and what type of food items are you looking for others to bring? I know the schools usually ask for families to bring a treat for their parties, or maybe you can just ask the children to bring X number of valentines to pass along to the others. And if it is snack type food, maybe you can ask for each person to bring a snack to share. But if you are thinking about serving a meal, then I think it would be best if you just served something simple like pizza and juice or something easy to make rather than asking the parents of the children to bring a pot luck dish.

I agree with bizlady. You're taking on a lot doing a children's party -- with crafts, too -- AND a potluck at the same time. I second the pizza suggestion (I think that's what we always did for our kids' birthday parties). In our experience, young kids don't eat much at the parties anyway, even the cake. They are too busy having fun. (Once we realized the kids cared a LOT more about the design on the cake than the taste, I stopped bothering to bake special cakes and just got an inexpensive cake from the supermarket.)

I also think it is asking a bit too much of the parents to have them provide a pile of valentine cards AND a decorated box AND a potluck dish, even if it's just a snack.

If you don't have the party at at meal time, the cupcakes should be plenty.

It is mostly three yearolds (parents will stay for the party) I think I will leave out the food part, it just felt like I was giving them so much to do just to have some fun. It is at 10:30. I'm not really putting an end time, usually when we do these everyone leaves around 1. I was going to have the cupcakes for the kids to decorate (plenty for parents too), chocolatechip cookies... maybe a fruit/cracker cheese platter? It is likely people will just ask if they can bring something and if they do I'll say okay.

Thanks for the help!!!

Actually when you said to bring something to "share" I was thinking more along the line of bringing the family pet or favorite book or game. Food never entered my mind!!!

Kids this age have a very short attention span. I would suggest possibly decorating one cupcake each, with very simple sprinkles etc, remember any food will get all over, even with parents.
Then some about 2-3 fun/singing/active games. Then pass out valetines--again short attention spam and you will have problems with 3 year olds decorating anything. I would suggest a large 8x11 envelope, and you could buy some at Walmart etc reasonable. Let them color etc Don't forget drinks. Juices with straw are good. Keep it simple and short. Plan for about a hour, but no more that two.