Activities for preschoolers in Bangkok

I'll be moving to Bangkok early July with my husband and two kids (1.5yo and 4yo). I'm going to be alone with the two kids 3 or 4 shorts days after our arrival and therefore, will be looking to entertain the two with fun activities.

Any suggestions on where to go? Good playgrounds indoor or out? Fun museums? Playgroups I can easily join?

Other than Siam Ocean World and the playground at the Emporium... I'm not sure where to go!

Thanks for any and all input! :)