Community Centers are great places to book a swimming party. If you can, utilize a scheduled family swim hour or if that isn't feasible then ask if you can book the whole pool and invite your children's friends' whole families for the swimming part. Most Community Centers have rooms you can use for the party part.  Ask if you can book a room. If there isn't anything available at the center, what better place to go than to a seafood restaurant like Red Lobster! Invitations: Shape them like buoys, safety jackets, or tubes. Treat bags: Beach toys, Ice Cream coupons, "Life Savers" candy, Frisbees, Water tubes...