That's admirable, but as has been discussed already, its not correct. You are causing problems for me next week when I do it correctly, because, all I will get is "last weeks ref never did that".
There is no allowance for retaking foul throws based on age in the LOTG.
It might appear common sense and make you out to be a nice friendly ref, however, its not what the LOTG dictate, and then we wonder why folk moan about consistency, well this is why ! Because referees simply go around making up their own rules !
Surely the best way is to allow the "foul throw", and make it clear to the player on his next throw that "keep your feet on the floor this time please" or whatever phrase is apt. Even then, you are not duty bound to penalise this one, but as you rightly say, most folk will support your third one.
Just stick to the LOTG, that's why you wear the badge and that's why a league appoint you.. It makes it so much easier for any referee who does follow the LOTG.