Hi,
How can I put it right?
Teaching to a class ( in which the neighbor's children study / with the neighbor's children /... ) can be difficult.

Thanks in advance

A teacher teaches a class, not to a class.

I would say "Teaching a class comprised of the neighbor's (or neighbors') children can be difficult."
Or "Teaching a group of neighborhood children..."
Or "Teaching neighborhood children..."
Simplicity is usually best.