I have some of those right now. They were sold as aponogeton ulvaceus (which they are clearly not). When they put up one of those baby bulbs, I've always just let it grow as big as it would get. Eventually the stem that it's attached to yellows and falls apart, and then I've planted the sprout. I've never gotten as far as a second generation with them, but the new plants have grown to a pretty good size.