by Gnipp
This is one of my 7 year old daughter's favorites. What I do is always situate myself as the last player so that I control the environment & villain decks. She loves to read the environment cards as they come into play. Sure, she may not understand every modifier that is happening, but I give her the brief versions and she follows along great.A big help was when she found someone she liked to play. It started as "The Wraith" and now when we play she is trying to figure out Unity. I switch up every game and most of the time let her choose. We also know the villains we start with. Baron Blade is a great villain for a beginner. I know you try Apostate and there is a lot of things happening there.
As for the card holding, a couple of years ago I made my daughter a card holder. I'm no woodworking master, but I found some spare oak at work and made a 3 step piece of wood with a simple sawblade cut on each shelf about 3/8" deep. What I ended up with is a heavy piece of wood that she can store about 15 cards on if needed. She used it for a while, but now she wants to be a big kid and doesn't want to use it anymore. Your other easy option is just play them face-up on the table. It's a co-op game, so he doesn't really have to hold his cards.
It's a long ramble, but I love SOTM and so does my daughter so I thought I mention our history with it.