I've been trying to find such games for my kids (4 & 6) - there really are no search options to help.
Indiscriminate third party advertising and freemium games are going to cause significant long-term harm to mobile gaming, and possibly also to society as a whole.
There's still some games out there that use IAP in small doses (<10 total) to sell reasonably sized chunks of content, but they don't make the money that freemium games do.
(My own device operates on the same rules as my kids - no third party advertising, no freemium IAP stuff. There's really nothing to miss in that space anyway…)
Not sure about iOS but on the Play Store you can look in the "Premium" section in Games.
Not all are IAP free, but it seems most of them are.
I've tried looking for games I could buy outright. Try finding a game without ads or in app purchases. It is extremely difficult to search by those criteria.