When are you planning on going? (If it's during Spring Break, I'd avoid Cancun at all costs (with kids). Playa del Carmen would be a much better option during that time.)
I'd definitely recommend the IB* resorts. The Maya and Lindo aren't the least expensive, but you'll have access to the Beach and Del Mar resort as well, which are next door. The Beach and Del Mar cost less, but you'll only have access to that resort only.
I'd also look into the Tucan/Quetzel resort. In Cancun proper, I'd check out Dreams. It won't be the least expensive, but there's plenty to do. Also check out the Now resorts (owned by the same company that owns Dreams).