Your bathroom seems to reduce in size as your family grows!
Try a few space saving ideas:
Attach additional towel rails on the door.
Encourage your gang to hang their towels there instead of on the floor!
For the extra supplies you need for the bathroom, like disinfectants, loo rolls and soap, etc., get the handyman in your household to put a fairly wide shelf just above the bathroom door.
That way they will be available when needed but won’t get in the way of everything else.
If you are really pressed for cupboard space, a plank across the bath will hold your shampoo, bubble baths, sponges and soap dishes.
Make sure the plank is sturdy and fairly immune to splashes of water.