F.C.
My 5 year old daughter does exactly the same thing and has been doing it since her teeth came in. She has had some dental work starting at 2 because of calcium deposits while still in the womb so she has been to a pediatric dental specialist for 3 years. When i asked him what to do about the grinding he said that i should not worry about it because they are baby teeth and the teeth are not broken. Once her permanent teeth come in he said she will probably need to get a mouth guard made for sleeping. So for now we just have to deal with the terrible noise.