Hi there,
I know this situation well as I have a 4 month old pup who does the same with our 7 year old - the adult food is much more appealing!

I guess they are just like us - when we were kids we always wanted to grow up fast!
I have seperated my dogs when they are fed before - ie: one is outside for a sniff and toilet whilst the other one eats inside and vise versa although the pup is now starting to realise as Ebs (our older girl) tells her whats what! I think and hope your top dog will eventually tell your pup what he/she can/can't do.
Good luck!
