@kjrc,
Note: I am offering this as friendly advice and am not acting in the capacity of an attorney to you.
Get yourself a divorce lawyer. Even if you think you will not file for divorce, you need to be prepared in case it happens. Tell the lawyer that you want a formal separation agreement set up, with you being the custodial parent but with your wife having full visitation rights,
if that is what you want. Show proof that you have had the kids with you (this means not photos but rather things like grocery bills) and that she has not.
Divorce lawyers are expensive and they charge by the hour, so be ready before you walk into anyone's office. And, yes, they are expensive, but having this set is going to be worth it. You may end up going to Family Court (not Circuit Court; the only Circuit Courts in New York are Federal appellate courts and they do not have jurisdiction herein) even if it isn't an actual divorce. The courts will act in the best interests of your children and, if you have been their sole care provider for the last three months, that looks good for you, but if your wife was their sole care provider for years before that then things will not be quite so black and white.