The pool my kids learned how to swim had a tot dock, it was essentially a metal table, think of a 5'x5' square metal table about 2' tall made of stainless steel that sat at the bottom of the pool. The kids that were too small to keep their heads above water stood on the dock and took turns with the swimming instructor. The top of the docks made of that diamond plate steel so it had some grip. I dunno if this design could be modified into something or maybe not.