Which is correct: “get” or “to get”?

Question

All they can do is get their children admission in any school and pay the fee for them.

or

All they can do is to get their children admission in any school and pay the fee for them.

Which one is grammatical?

Answer 1

It all hinges on "can" in this case:

What can they do?

They can get their children admitted in any school so long as they pay the fee.

You can't say "They can to get," can you? Et voila.