From the ELL SE post am I a native speaker?
So I literally grew up with their kids and they taught me English and my brother and I would teach them Portuguese (I'm Brazilian btw)
After reading the differences between used to and would when talkng about habits on the bbc web, I think used to would be more appropriate as teaching is not something you do many times Once the learner speaks fluently is finish
Would is fine in this context because the time frame has been established as being in the past. Used to can still be used here, but would sounds more natural in this instance. It's only when you remove the time frame that would no longer makes sense. Compare these sentences:
Do you see those kids? I would teach them English.
This means that you would teach them English if you had the opportunity.
Do you see those kids? I used to teach them English.
This means that in the past you taught them English.
However, once you insert a phrase establishing the time frame being in the past, the first sentence can be made to mean the same as the second.
Do you see those kids? They grew up around the corner from me. I would teach them English.
