Both my kids (4 and 7) use fire tablets and we have the subscription with it to get them access to lots of free apps.
I put memory cards in both, as what they come with is insufficient. The older versions we had were a little janky, but we haven’t really had any issues with the current ones.
The parental controls could be better but work okay. In the kids version of the interface you don’t really see ads, just app recommendations. Some of the apps still have gated content, but it hasn’t really been an issue.
I’ve been playing Palia. It’s a chill MMO focused on resource gathering, NPC quests, and crafting.