Pool plaster is best polished with smaller pads 5", 7" or slightly larger with a flexible backing pad. There are a lot of curves, coves and detail work in a pool that a 20" floor grinder would not polish, the rest would have to be hand polished.
Some times old pool plaster is very thin, then when you polish it you go all the way to the gunite. I would plaster the pool or buy the kids aqua shoes to wear in the pool.
Hope this helps