You're absolutely on to something. I witnessed this firsthand recently. For myself I got in under the wire I think. I grew up hearing the reasons why my parents switched. I remember our NO church and the differences were active discussions in our home. And they were active discussions based on experience, not an imaginary boogeyman.
What I saw recently was several young people who were raised SSPX and have no idea what the NO and its liberal errors are like. Because they have no concrete experience, they were completely unable to detect it coming from their SSPX priest. I am not nit picky and wanting to grasp any little detail to accuse the priests of being liberal, this was a very serious subject and with several people repeating the same thing independently of each other, there was no room for error in my understanding. It was a shocking eye-opener for me, not only that there really are liberal priests in the SSPX but that cradle trads are so trusting and defenseless against them.
We move our families to SSPX parishes so they will have good influences, good schools, good friends, and some idea of what a Catholic society is like. It's so important. But, how do we not shelter them so much that they cannot spot the errors anymore? Even if they are strong in their Faith, if they are too innocent then they will fall for anything as long as it is cloaked in persuasive Catholic language. Society was Catholic at one time, right? Yet it still fell. I think we underestimate how attractively wrapped these errors are when fed to Catholics. And we underestimate the power of the slow boil. We're too quick to dismiss the little things. "He that is faithful in that which is least, is faithful also in that which is greater:"
So it seems like cradle trads really do need a little inoculation through the years. Before they leave the house and fall in head first on their own. They don't need worldly inoculation but some small exposure to the philosophies and the errors so they can recognize them when they see them, no matter where they show up, even if it's from an SSPX priest.
I see the problem but I don't know what to so about it, practically speaking. Do you bring older kids to a NO mass once in a while and have discussions afterwards? Do you listen to NO sermons together and point out error and/or ambiguity? How do you get them to see it with their own physical and metaphorical eyes without tainting them or weakening their Faith? It's definitely a difficult exercise in the virtue of hope.