If I can't buy it or get it free without ads, it doesn't go on the iPad (I test with my iPhone if I'm unsure), and thus my kid isn't exposed to it (device is locked down tight to prevent purchases/etc, and I sync the apps on there after they've been reviewed by me).
I had a 7 year old recently ask me about dieting and weight-loss strategies because of an in-game "one weird trick to lose weight" ad.