Fixture hookup. The final step is for the plumber and electrician to return to install the various fixtures and make the plumbing and wiring connections. There is an inherent hazard with any plumbing and wiring work, but when pros have run the plumbing and wiring inside the walls, the final hookups are well within the skill range of experienced DIYers. Make sure, though, that the final installation is inspected.
Children: Small bathrooms for children may need to endure decades of use and abuse. Small kids need a bathtub; showers are useless. Floors are most important since little kids can flood bathroom floors with water simply by stepping out of the tub. Good durable fixtures and waterproof floors and walls are essential for bathrooms used by kids. Good storage is essential here, too.
Tile the walls first, then the floor. When tiling around the window, keep the tile about 1/8 in. away from the glass block. Tile the floor, starting by carefully snapping center lines to lay out border strips and field tile. Work from those lines to get evenly spaced tiles throughout the floor. Grout the walls and floors but caulk the inside corners between floors and walls and where walls meet.
The cheapest route of all also typically the one that takes the most time: doing all or most of the work yourself. A very (very) skilled DIYer with plenty of time and a group of willing friends and helpers may be able to finish a bathroom remodel nearly as fast as a general contractor, but very few homeowners fall into that category. And there is the issue of quality: good contractors will do the job professionally, while many DIY installations will be recognizable as the work of an amateur.