First of all. Relax.

Take deep breaths. Walk a lot. Even if it is around in circles. Get soul food. Whatever it is that makes you feel good eating it. Force yourself to eat regularly.

For me, I meditate often through the day when faced with such tense situations. The basics of meditation is to stop the chattering in the mind. This stops all the worry for a little bit allowing you to reset.

You have already made you decision.
And it may be the wrong one, but you have decided to leave them in school with the grandparents.

Now you will have to ride this one through.
It may turn out to be the wrong decision.
However, any thoughts in solving that area of doubt are in the distinctly criminal, and thus, the children's future lives will be destroyed anyway.

So, there is nothing to do but make sure you stay in top physical and mental shape.

You may try getting burner phones for the kids and tell them to message you if ever anything at school happens out of normal. Such as being called to the principals office.