I find the Bible stories about the childhoods of both Moses and Samuel quite fascinating. In both cases, the mothers only had them until they were weaned. Common opinion of the times was that it was between 4 and 5 years of age. At that point, both were sent into either pagan or dysfunctional families. Moses went to Pharaoh and was taught all his life about Egyptian gods. Samuel went to live in a home where the father had raised embarrassing reprobate sons whom God eventually killed for their sinful ways. Yet both boys grew up to be devoted, passionate servants of the Most High God.
The take away is that whatever faith those mothers deposited in the hearts of those two preschoolers lasted them a lifetime.
Never leave to chance nor take for granted the spiritual mentoring you do with your children. But be deliberate about their training. Start very young. Assume nothing. Bathe them with prayer, worship, and the Word. The fruit of your labor will be everlasting.