Main Drain Question

I have a 12x24 inground pool w/ a deep end. It has one skimmer, a main drain and two returns (one of which is hooked to a fountain). Bought the house w/ pool already there. Have maintained the pool for about 4 years now. My oldest child is now old enough to dive down to the deep end. I have an anti-vortex cap on my main drain. After doing some digging, I have discovered there is now an "anti-entrapment" drain cover as well (even required on new builds?).

Questions:

1. is my anti-vortex good enough for keeping inquisitive fingers/hair out of the drain?

2. If I choose to replace cover, can I do so w/ water in the pool?

3. With young children using pool, should I even keep the main drain on? I have a valve I can close.

My pool is "indoors" in that it has a sunroom built over it. It has 6 skylight type windows in the roof, but w/ trees and such keeping most sunlight out, I don't usually have a problem w/ chemicals staying put. I have a cartridge filter system.

Thanks for replies!!