I can answer this one! Kids are 5, 8, and 10 here and we've had multicades at home for 3 years now.
I've had several muticades over the past year and based off of what you've said will tell you the following. People will tell you anything can be configured, but this is based off of my experience. Others will tell you to do this yourself.
Best choice: Get on facebook marketplace and buy a retropi based Acrade 1up. People will convert the arcade1ups to run retropi. With these builds you can play pretty much any non 3-d arcade game and all 2-d consoles. You could get one for around $800 if someone local builds them and it would be 90% as fun as a multithousand dolar custom mame build for the kids. Limited to 2 kids at a time. Here is my old ad from when I sold mine (wish I still had it). https://pinside.com/pinball/market/classifieds/archive/90621 Easy enough for 6+ year olds to pick out games and use them without getting stuck. Most things worked.
Easiest choice to do yourself with a ton of games if it is you playing it: Converted Atgames Legends: This is part of what I have now. Buy the cabinet at Sams, order a thumb drive with a gazillion games off of Etsy (CoinopsX). You can set up the extra games in about an hour. 6+ can generally use it without help, but it may require an adult to get it back on the expanded games section if the power is turned off. See here for someone elses thoughts https://pinside.com/pinball/forum/topic/multicades-i-am-hooked/page/3#post-6597393 So far 100% of games I have tried have worked without issue. Atgames legends without the adon is complete garbage.
Worst Choice: Custom Mame build. I lucked into one for free and it was awesome. Kids absolutely could not use it by itself. Only thing that played 3-d games. Had to sell it because I could not get all of the porn off of my custom build (got it for free from company office for same reason). Here is the ad and review from when I sold mine. https://pinside.com/pinball/market/classifieds/archive/113108
Easiest for kids to use: Hands down the arcade 1ups. I have some 1ups set up next to my multicade and the kids play the 1ups way more (outrun is their favorite right now). I have 2 currently with 1 on order. 1 has been converted to a 60 in 1 but my youngest can't work it himself. 4+ year olds can use and select games from arcade 1up with no adult help. It will take you 2 hours to put together the 1st one you buy and 1 hour for each additional one. They are also surprisingly easy to sell/trade and they hold most of their value (so far). Here is a for sale of 1 I just sold. https://pinside.com/pinball/forum/topic/pacman-arcade-legacy-1up-12-in-1-pacman-galaga-dig-dug#post-6550461
Here is the old lineup.
Have fun!
Happy to answer any questions
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