It is very serious, and is more so the more strict your parents are.
For instance, some parents are more liberal. Those are the ones that let their kids stay home from boasting sessions if they have a test or homework to do, allow them to participate in after-school events, drive around to look at the Christmas lights, and are not unreasonable when it comes to music and entertainment. The ones brought up in such households are not as likely to be severely affected, as they usually get enough experience to function outside the religion. They also think it isn't all that bad.
However, you get other parents for whom the religion is everything. Christmas comes, and they are not even allowed to look at Christmas displays. When at houses in field circus, they are not even allowed to look at the TV or whatever the householder has in the way of toys and decorations. They have to pious-sneer every vacation from school, and can't even join their classes on field trips. There are 225 135 songs they can listen to, and they cannot watch anything except videos from the Filthful and Disgraceful Slavebugger. Sometimes, they don't even have a TV or radio. They are not allowed online, for any reason or at any time. They can't even have anything to do with outsiders except to make them become witlesses. Their careers are pious-sneering, becoming hounders, and Beth Hell. Those are the ones for whom everything is a drudgery because they are always out in field circus, even on Christmas Day.