Mouthing

My two have taken up a new lil' game between em' .. It seems while skye is on my lap and vinnie is lay next to me Vinnie will open his mouth and sky will start nibbling at his teeth and his mouth and cheeks etc and then vinnie will start to nibble at hers, Vinnie not knowing how big his mouth actually is has to be told to stop at times because her whole head can fit in his mouth lol!
Is this a normal behaviour between two dogs? .. he dont bite her he just nibbles her, even when she is grabbed onto his flabby cheek skin! lol
We have decided aswell because skye is so teeny, we do monitiored play time on the floor, when vinnie starts to get a lil' too rough we end it because he doesnt understand why she cant play as rough as he can lol, we never leave them in a room alone and if skye gets too excited and winds vinnie up she goes in her crate but if vinnie gets too excited and rough he goes in his is this right?
Its usually skye winding vinnie up to be honest because she makes loads of noises when playing lol... i personally think the bigger she gets the easier it will become for them both to play togethor?? because currently skye is just bigger than vinnies head!! lol
Any Tips and advice greatly taken on board

I just see that as playing...lots of dogs do it.

Your right not to leave them alone together as they can have a fall out in a matter of seconds and staffies can make a mess of each other should it happen.

Hoping we will have some pups soon too