I think this is a good thread to maintain, given what I suppose to be the age of many RPS readers. I am certain some of these have been mentioned above, but a few that have been good with my oldest over the years (obviously these depend on age, but all are arguably suitable for children of some ages, given the cartoon nature or what is likely already out of the stable!):
Doorkickers: Action Squad
Castle Crashers
Overcooked
Ultimate Chicken Horse
Lego games - the ‘best’ one IMO was the first Marvel Superheroes game. Second also ok.
Sonic All-Stars Racing
Gold With Your Friends
Lethal League
Trine (1,2,4)
Knight Squad
Goatr Simulator
Speedrunners
Lovers In A Dangerous Spacetime
Nidhogg (1&2)
Magicka
Broforce
Stick Fight
Pummel Party
Duck Game
These last four have given the most value by a distance, I think. I can’t rate Pummel Party highly enough, given the price and the support the devs have given it. It has the odd quirk, but mostly it’s fantastic!