That was exactly what happen to my kids yesterday. I don't mind ads, but when they are inappropriate for the 5 years old I get really pissed off. And I wish Apple Arcade could come sooner so they don't get distracted with Ads.
It is the same reason I don't really allow them to watch Youtube unattended anymore. I wish there is some curated Kid Channel I can safely let them browse. ( Kid these days are extremely good with technologies )