S.R.
Have you tried putting both children in the tub together with their toys? With my 4 y/o she took baths with me out of necessity and then I couldn't keep her out of the bathroom until my youngest was about 5 mo old and they started bathing together. Even though you have one boy and one girl, they are young enough that I don't think there is anything wrong with them bathing together. Best of Luck, this too will pass (as they say) :)