My partner's ex-wife re-married in California 10 years ago. She had 2 children from her first marriage. She passed away unexpectedly in July last year. She and her husband had Wills in which each left their assets to the surviving partner. Nothing was left to either of the 2 children - can the children make a claim against this Will?

I doubt the kids have any recourse. So, I would say, no.

When you say nothing was left to the children were they mentioned at all ?