There are two bolts on the door from the bedroom to the front garden with the pool, one at the bottom and one at the top, so you use that to prevent toddler access.

There is another route to the pool via the entrance door to the bedroom. You could lock this. The lock is at about 1m height from the ground, so probably not reachable by a toddler.

However, the desk area in the room is sunken. Your seat at the desk is at the same height as the floor of the rest of the room. There is the possibility that a toddler could fall into this area. You would need to get a guard put round this.