It's possible that you don't have enough space for that exact move.
Don't take my word for this 100%, I'm unsure of it myself.
>Prior to Generation VI, if the father knows any TM or HM moves (and in Crystal, Move Tutor moves) that the baby is also compatible with, it will inherit the move
>If the father or (starting in Generation VI) the mother knows any specific Egg moves that the baby can learn, the baby will inherit the move. If the parents both know different Egg moves, the father's Egg moves are passed on first, then followed by the mother's.
The only explanation I can come up with right now is that the parents know some TM or HM moves the offspring can learn, along with the father knowing any possible egg moves(for example Mud bomb) and the offspring just doesn't have enough moveslots to learn Avalanche.
If you have any more info, tell me in the comment and I will help you and edit the answer as needed.
Otherwise I don't think anything can prevent it. :/
Hope I helped.