As I have no children Grace , that scenario won´t happen.
But if I had a kid and he would express those desires to me , first of all I would be very
proud of him for having the courage to tell me ! and give him a big hug.
Then I would reasure him that it´s allright to have those feelings , that there are many childen out there like him and that he should be who he wants to be.
Over the years I would let him discover himself on his own , and when he gets older If those feelings are still there , and even grew stronger , so that maybe even transitioning would come into the picture , I would support him with that also , giving him advice as much as I can.
Then , after his 18th birthday , I would probably tell him that : I have a big secret I want to shear with you , and only you , your dad has been crossdressing since childhood…. and that the apple didn´t fall far from the tree apparently !