Ehhhh... I thought I mentioned Nirwana resort already???
Big resort with many activities, got 2 swimming pools, right at the beach, also got 2 sister resorts next to it and one of the cheapest resorts in Bintan...
If you prefer something more high class, you could always go to Banyan Tree Bintan Resort, Angsana Resort, Club Med Ria Bintan, Bintan Lagoon Resorts etc.
Club Med Ria Bintan might not be a bad option though as it definately has many activities for children.