Unable to conceive children and desperate to be a mother, a gifted young teacher comes to work for a family that has been beset by tragedy and serendipitously changes all their lives for the better

This is what I’m able to glean:
“A barren teacher …”

Teachers – known to be swimming in kids 😉. How's this family is going to provide a fix for her “desperate to be a mother” situation?

Show don’t tell the tragedy and her goal. As a reader, you cannot envision what “change all their lives for the better” will look like on the screen.

Hope you find this constructive, keep going.

*widower man (of course)

I think you have to work with the word “comes to”… this has to be a something she has to do … or else…

So maybe something like..

Unable to conceive children and desperate to be a mother, a young teacher loses her job and therefor comes to work for a man and his disciplined children while he looks for a suitable wife.