I have known many mothers (and fathers) in my lifetime.Some worry a great deal about what their kids are up to. The main worry for parents whose children declare a belief is that of the "weird", brain-washing cults; and there are many of them!I have also heard many a mother make a remark such as, "She'll grow out of it." or "It's just a phase he's going through; he'll forget it when he grows up."
Only one ever came screaming to the Pagan group, shouting that we had "seduced" her 20 year old daughter!
If you tell your parents, honestly and gently, that you haven't changed, that only your beliefs have changed, they will usually accept it. Of course, many will also try to tell you that you are wrong; some even forbid! But that is their fear! And understandable. So, if you are sure your parents will object, keep it secret until you are older.