Rollin In The Heep
Out east on Long Island is the Harbes Family Farm, where each year they hold a Sweet Corn Festival. This year my son and I went, mainly because he loves the grounds and all the children-friendly items.
This is a great spot for children's portraits because its not typical, yet not really distracting. If you have a client who is more toward the country side, I would suggest finding a farm similar to Harbes - if not Harbes itself - and photograph the portraits there. Just remember to ask the owners if you're allowed to photograph on the grounds... and bring business cards!