If you’re going to do that anyway, I’d rather make it a relatively full second bathroom, otherwise you can hardly dry yourself. Not to mention storage for the various beauty utensils teen girls "need".
The kids' bathroom is the same size as our (only) bathroom currently in the rental apartment. I actually find it more than sufficient. Of course, it depends on what you’re used to, but I don’t think it lacks sufficient space. But I guess it depends on the habit.
The solution with the washing machine upstairs is quite nice in itself – but now you have the balcony at the kids’ room again. One more question about that: Where will you, or where will you all, iron or fold the laundry?
Yes, I need to think it through completely. Just a quick thought: If I have to do laundry downstairs, I carry all the laundry down and back up. Both laundry that then goes in the dryer and laundry that I hang up. I really mostly have dryer laundry. I’d rather go down occasionally in summer to hang the small amount of line-dried laundry in the garden than constantly lug everything down – I’m thinking of bed linen, towels, etc. Also, the lower level area is more importantly spacious to us than the upper one – I would have to enlarge the utility room downstairs and shrink the kitchen for the washing machine. The house really isn’t overly big but I’d rather save the space downstairs than upstairs. Sure, the kids then have the “bad luck” with the “small” bathroom – but I think better at least a bathroom than none. However, I don’t really like the washing location now either. I’m open to suggestions. I just really like the layout of the master bathroom PERFECT as it is, otherwise I would have thought about somehow fitting it in the bathroom. I just wouldn’t know how... oops: To answer the question: I would iron and fold in the bedroom and hang in the bathroom in winter.