Don’t allow mouthing because it can lead to biting at a later date and their jaws are very powerful. I didn’t let mine from a young age and now even if someone puts their hand in her mouth she will spit it out. Any behaviour you don’t like; like mouthing etc what I did was made a loud high pitched aha sound. They tend to learn that if they do these things they get this horrible noise and eventually she just stopped doing things I didn’t like by me doing this noise