Parents often have a hard time finding the right balance between giving advice and keeping silent when their children get older and have their own families. Someday you'll probably face the same situation with your own children; almost every parent does.
In other words, try to understand your mother's actions even if you occasionally find them irritating. No doubt she loves you and your family, and even if she intrudes more than she should, she still cares for you and wants what is best for you. Go out of your way to show gratitude when she is helpful, and even ask her advice when you think she might have something to offer. When you do reject her advice, therefore, she won't think you are rejecting her.
Then learn to evaluate her advice without dismissing it just because it comes from her. Even bad advice sometimes contains a kernel of truth! More than that, ask God to help you raise your children the way He wants you to. God has entrusted them to you, to help them grow physically, mentally and spiritually.
Finally, tell your mother that while you appreciate her concern, you can't always agree with her. But do it gently and in love. The Bible says, "The quiet words of the wise are more to be heeded than the shouts of a ruler of fools" (Ecclesiastes 9:17).