I haven’t tired it with kids but I would ask how they are with Lego? Do they like to follow the instructions and build it up or is it more grab pieces and build shapes?
You have to build the rockets the right way for them to go anywhere and there is a lot of hit the right button at the right time kinda thing but if the kid is into building things and likes instructions then Kerbal could be good.
There are decent enough youtube playlist for getting started. First one is a few hours long but he gets to the Mun after a couple of hours and the second one is by Scott Manley and is sciencey by a big space nerd.