We took almost a month, drove from Singapore and went to the following places with 2 kids aged 3 and 5, thought would share a brief review...
Sibu Island Resort - highly NOT recommended, evil sandflies, expensive and basic living
Summerset, Kuala Rompin - so so, went to break journey, good value.
Impiana Cherating - recommended, good value, at cherating must try batik painting and see the fireflies, kids absolutely loved it and hard to screw up batik painting (wish they had it for b'day parties here)
Gem Island - HIGHLY recommended, really a hidden gem, they have a turtle sanctuary, good value, good food, good service, nice pool, nice beach.
Riyaz, K. Trengganu - still new now but not sure after a few years, too quiet overall but got to see a giant swamp lizard. KT has a good market place, museum and big big children parks.
Pulau Perhentian - we booked last minute into Bubu, the place was basic and expensive for the value but the snorkelling sites for the kids were absolutely great.
Tasik Belum resort - nice hill getaway to see world biggest flower.
Penang - Gurney Drive hotel - 2 bedroom apartment for M$250, v good value incl. breakfast.