My experience is more with my grandmother, and its from another angle; she blames every single person in the family for everything EXCEPT me, probably because I'm the only one in the family other than her two sons who speaks Portuguese with her.
It can be very difficult to say what you want, but accompany most things with a smile and it softens every word. A lot of my defending my parents and uncles involves me simply smiling and telling her that they're simply raising the family in a way that makes sense for their situation. You're going to have different issues with your kids than they had with you, and you just have to calmly explain to them that you're not ignorant of the things they point out, but things are the way they are for a reason.
If you need to make a stronger point, you can tell them their advice to you about how to raise your family is about as well-informed and appropriate as you telling them that they are too old to do this or that and that you're making the decision to fix it by doing _____________.