They're decent in terms of size. Like most kids' meals, they tend to be not so good in terms of variety. Some places have kids' menus listed, and some do not, but still have them. The other issue is availability - or at least visibility. When we ate at Simpson's Fast Food Blvd, there were no kids' menus listed. The TM directing the line told me there were no children's menus, and encouraged us to order something stripped down off the regular menu. I disagreed, and one of the TMs serving the food confirmed that the kids' options were chicken tenders, personal cheese pizza, and something else - fish maybe? - I forget. But anyway, you specifically have to ask in some places.
And it's not QS, but when we went to Mythos, there were no paper menus, but the QR code on the table took us to an online menu - adults only. I just googled the kids' menu, and it popped up and we ordered from it, but again, I only knew it existed because I'd done research on kids' menus before going.
I will say that if your kids order from the kids' menu and you stick with water instead of pricier soft drinks, the cost of TS is roughly equivalent to QS. You write that you are familiar with Disney, so perhaps you are thinking of the pricing of their TS meals, which is far and away more expensive than QS. I encourage you to look through the Universal TS menus because their prices might pleasantly surprise you.