Since you have a girl and a boy, it would be a good idea to have the option of a split facility concept. Depending upon WHERE THE DOOR IS LOCATED, OR IF THERE ARE TWO DOORS....IS THIS A JACK & JILL BATHROOM? You know, is it between two bedrooms? Or is it accessed by a single door from the hall?

What my best friend has is with the door coming off the hall on the narrow end of the room. It would be possible to do this with a 5 foot wide room. Have the door to the side of the 5 foot dimension so you can have the most depth for a double vanity. THAT is the thing which will be good as your kids grow up, having a set of drawers all their own. It could be side by side in between the two sinks. You will not need BIG SINKS, so think smaller. Think one large mirror on the wall and NOT separate medicine cabs, since the kids won't be able to reach them now anyway. NO linen closet in the bath. Towel bars on the wall opposite the sinks.

At the end of the two-sink vanity, have a door. It will be lined up with the entry door. There will be a toilet just inside the tub/toilet area. The door will open from left hand inward. There should be enough space for it to swing flat against the wall, maybe a 28" door width is enough.

Then a shallow soaking tub will be tiled above with solid material tub enclosure, not individual tiles, have a hand held shower head if you must, a floor drain if you think it would be a good idea. NO glass doors at their young age, it could be a safety hazard. But consider it for the future.

Having the bath and toilet split that way allows for more use and more privacy also.

Choose a train style towel rack for storage of extra towels. When you have the walls built, make sure there are plenty of BLOCKS inside the walls so that any child hanging off the towels will not rip a hole in the wall. If there is a window in your option, either make it Lexan or put it up very high on the wall.

I think a 5' long tub would be fine. If you have the 6' easily done, then make the bath 6' wide. I'd still put a 5' tub in, and 30" wide maximum. The extra 12" at the end of the tub could be open shelved storage inside the tub/toilet area, and give some more knee room when someone is sitting on the john.

Also, it would give more "swing" room for the entry door near the first vanity and sink.

Here's a floor plan I copied from this forum for a 5 x 8 feet bathroom with no window. My space is 5 x 7 and I could not find any other way to fit this all in and I really wanted to keep a tub since it's the only tub in the house. Fitting the split idea described above just seems like it won't fit in the super small space we have to work with. I custom ordered a 22 inch x 18 inch deep vanity to make more room, and the Toto toilet is the most narrow one they make.

That is the exact floor plan which was in my little MoccasinLanding cottage. And I was thinking split concept, not remembering just how short seven feet really is.

Keeping the plumbing on one wall will be much better, since most plumbing walls have need to be deeper than ordinary walls. Cheaper to build it too. If you do have the extra foot of width to give this bath, it would help prevent a cramped feeling. I still would say no sliding shower doors, because they make it awkward in a small bath to bend over the toilet to turn on the tub.

In our extremely tiny bath, we chose the American Standard Cadet 3 COMPACT ONE PIECE toilet, with 1.24 gallon flush. It has never failed to flush with one try. It is Water Sense qualified. We got the elongated version, not the round front, and we are very satisfied with it. It has a very small footprint.

I would not have two sinks for a boy and girl sharing a bathroom. Separate storage for each, yes, but not two sinks. They will never be in there at the same time once they are a little older. One sink, adequate counterspace and some personal storage: that would be more important that two sinks.