I own both Iron Maiden and Avengers IQ pros…they are both pinball masterpieces in my opinion. No matter which one you get you will not look back. Both have deep excellent software and original playfield layouts.
The Iron Maiden will be easy to pick up for your kids rules wise, but very hard to finish. The Avengers comic book theme will probably appeal to them more, but the software is quite complicated at first approach, with moving gems around, as well as defending them. I had a near perfect game to finish the 5 Wizard modes.
You can’t go wrong with a Keith Elwin pin, best player and amazing designer.
Great luck with your search!