If they found out their child was trans, many transphobic parents would retaliate by abusing them physically, verbally, destroying their belongings, isolating them, evicting them, etc. Kids should have the choice to keep their parents in the dark, which makes sense especially in this case.

If a child feels more safe coming out to their teacher than they do to their parents, I think they should have the liberty to not be pushed into unsafe homes. Whenever they feel comfortable, if they feel comfortable, they'll themselves tell their parents. Their identity is not yours to disclose.