Second - people, we are here to read a comic about stick figures, for goodness sake!!! Hello!?!? Pots and kettles!
Um. You're comparing two completely different things; there's nothing childish about the OOTS style of drawing. It's just very simple, getting rid of non-essentials so as to concentrate on the characters, the story and of course the humour. The childish humour of Erfworld, by contrast, is intrusive; evidently some people like it and some don't, but either way, you can't ignore it.
"When the captain of the Titanic saw the iceberg coming, he didn't panic. He drowned." -- Paul Merton