Children At Wedding Dinner

My daughter is getting married next August. We have many small children in our family and both sides of the families are extremely large. The children are invited to the ceremony and Dance but due to the number of seats available we are not able to have them at the dinner. We are unsure of how to state this on a rsvp card. We plan on having a pizza party with a sitter in a room seperate from the reception. Any help is appreciated!