My son asked me if I would play league of legends with him, so tried it for the first time. So much going on!
Firstly, how does anyone zero in on what hero they want to play, there are so many of them! I feel like it would take a year just to play enough to decide.
Secondly, the purchase UI seems to have been designed to ensure that a new player can never understand it. I’m sure like all things it becomes clear over time but jeez, did a professional team really work on that thing?
Anyway, 2 defeats from 2 games so far, I write to you from the lobby waiting for the third!
I would choose a character and concentrate on learning him. There are builds online you can use to not get over whelmed at first by the shop.
I play an other MOBA but there is probably a lane that has two players for most of the match, you should concentrate on playing one of those two types of characters so you and your son can maximise play time together, most likely the tank would be the better choice (more forgiving, easier to learn, support character so your son gets to be the hero).