Eh why would he go cancel his children's medical insurance? Did he just choose to cancel it? That's pretty shitty. Can't legally have Medicare if there is a viable insurance policy, but they don't catch half the shit people do so maybe.

Is it that he lost his job and can't keep insurance? If that is the case, tell the BM immediately and work on getting a new job with insurance.

In MI a parent can be ordered to carry insurance, UNLESS the cost of the premium equates to a certain % of the parents take-home. I forget what that % is, but if the cost is unreasonable, usually a judge won't enforce it. You don't state the reason why your H canceled the insurance, but my guess is that if it wasn't due to the extreme cost, he may have just landed himself in hot water.

If he pays CS through the state, he can find out from the state whether she has them on Medicaid.

Stupid of him, not fair on the kids.