I think with kids that age (mine are right around the same) JP, MB, and AFM are the ones you would have to consider. They are all ranked in the top 5 on pinside. 2 of them have stood the test of time, and 1 is pretty widely considered an instant classic.

I dont really think you could go wrong with any of them. The real question is...what do your kids enjoy? If they like dinosaurs, it wouldnt make much sense to get a pin to share that has aliens.

My best advice would be to go to a distributer or a location when they open and play all with the family to decide.