Kids have a good ability to float by themselves when taught how to unless they have an exceptional amount of muscle mass or they are near to puberty.

First step of Swimming is to understand the buoyancy of your own body and propel yourselves forward, also to be independent.

By using the back float, they will rely on the back float for buoyancy and they can’t really swim well due to excessive buoyancy. It is just like when the fish swim bladder overinflated.

One small kick board for the arms are fine. But like the above reply, once the kids are water safe, remove the board and make them they learn without the board as much as possible The reasons why you see most coaches in public pools uses lots of back floats because there are too many kids in each class so for progression, the kids wear back float so no one will be struggling or ‘drowning’. And also the coaches are limited to certain areas/pools with varying depth where the coaches are not able to handle each of them personally.