Yeah the UI is pretty disastrous. No sounds in the shop at all. No ability to adjust the music and sound volumes. I usually play Isaac low with music on, but can't with this game.
I find adjusting to the different characters quite difficult. On the surface they don't look too different, but in actual gameplay style they are completely different. So trying to finish the game I do a few runs with a character, complete, then move on to the next one and have a huge adjustment period.
And I'm sorry your son is going down the Isaac rabbit hole. He will never return.