DY: That is because there is no flexibility in keeping ikar Halacha. There are work-arounds which may not be socially acceptable, but they do exist (and should be explored when appropriate). Even for an at-risk child, you can’t tell them don’t worry about Niddah today. You can (and perhaps should) tell them not to deal with Minyan or H&J, as that is not as critical.
My issue is more with those who insist on keeping Chumrahs socially than caring about the actual Chumrah itself, or the reason for it. (We certainly agree that a Yorei Shomayim has the right to implement Chumrahs and Gedarim for themselves. They show themselves by being “Machmir” where it is not popular, easy or showy (for an obvious example, not wearing a showy hat, tie or suit vs. making your wife dress like a frump because you are oh so Tznius (while you (the husband) are dripping with bling (or the top of the line Straimel) and making heads turn)).
For example, if a parents wants their child to do the right thing because of how his behavior reflects on them, the child will sense it and could rebel. If a father practices and teaches chumras out of genuine yiras shomayim, the child is likely to keep them b’simcha.
Hear hear!