I'd say tub shower combo for kids. and depends do both kids require bathroom at same time? or do you require more storage and one large sink. I think it's personal preference. I prefer large vanity with storage, large sink and more counter top space

I might try for at least one drawer for each child that is tall enough for a few toiletries down the line. Your oldest will want their things separate from a child 6 years younger before long. If all go at the same time to wash up for dinner or to brush teeth, then maybe two sinks or a trough sink with two faucets will be helpful. I would bet on whether they are all the same gender, as well. A lone girl or lone boy may want a sink separate from the "heathens" or the fussy girls. So many variables! Mostly, it is what your family habits will be. Do you teach them to go in that room and shut the door behind them, to leave one be while in the bathroom? Then the second sink is not as needed. If it is going to be a free-for all, old and young trying to get ready together, then the second sink is more needed.

1 bathroom for 3 kids who will eventually be teenagers together getting ready in the morning? I’d definitely do 2 sinks. My kids took baths until they were about 7 or 8, so I’d probably do a tub/shower combo.