Do I need to disclose to a woman who I intend to perform Mutah with that I have children from a previous marriage if she asks me? Or can I withhold this information?
Bismihi ta'ala
Because it is a temporary mut'ah contract, you or her have no obligations towards each other, so, from a shar'i perspective you do not need to inform her about your personal life.
Should this evolve into something serious, you must always try to be honest and straightforward with your circumstances and not conceal important information that would affect a relationship.
With prayers for your success.