chinuch and chumra

In an earlier post I raised the question of whether one should teach a child chumros, or wait until the kid gets older and either picks up the practices independently or can at least appreciate them better. I found in Shu”t Ad Nidbiru (vol 14 #33) that R’ Binyamin Zilber was asked this question in the context of a tefillin shayla. The Satmar Rebbe’s opinion apparently is that a lefty should put tefillin (after fulfilling the mitzvah by putting them on his right hand) on his left hand (like righty’s do) based on an AR”I – a chumra not brought in other poskim. A father asked whether he should teach this chumra to his lefty son who was near bar mitzvah, or wait until the child was more mature. Unfortunately for my purpose R’ Zilber spends the majority of the tshuvah disagreeing with the whole chumra, but in the last paragraph he writes that if a chumra is valid a child should keep it from bar mitzvah.