Like many kitten-owners I have always played with my hands,those little kitty-teeth don't really hurt.Everbody knows when I get a new kitten,my hands look like road-maps
Having said that,as they got older,no more hands...because then it hurts!!
Little kittens will chase anything that moves,incuding toes,I am sure a puppy would do the same,that does not mean they are aggressive or bad cats,just very playful and trying to learn the ropes and you have to teach them.
Never ever punish a kitten for being a kitten,aggression feeds aggression,if all else fails have a little mist bottle of water handy.
This tounge depression thing,I don't know about that,firstly if you put your finger in his mouth,won't he just bite down on it?It sounds a little strange to me,but if it has worked for you.....