Not to toot my own horn but I've been told my own webcomic "Question Duck" can have a soothing languid feel to it. So maybe I speak from a place of experience here.
Being child friendly can mean a huge range of things. From goofy http://sugaryserials.com/
. But I think the way you specify it, you're looking for something relaxed and quiet and frankly very rare in webcomics. Yotsuba would be a rare enough example of a printed comic. But even more than print, webcomics rely heavily on returning viewers and attracting new ones. You often can't get that by being calm and relaxed. Returning interest almost requires drama or gags or something that makes you want more to desire. And calm and relaxed by it's nature is complete. It is whole, and it is beautiful, and it is incredible. But people don't always feel the need to come back for more.
Short comics, short stories, or even single books are at their best when they provide a complete cycle. They are whole and they are wonderful. And best of all, they can end peacefully and calmly and people are all the more glad for it.
Ongoing stories on the other hand, require that extra edge that keeps people wondering what's next. What danger is on the horizon or what drama will the characters inflict upon themselves. Or for comedies, it's also about what boundaries you're going to push next. And by their nature, webcomics are mostly ongoing stories.
It's something like that. I'm not certain if I explained it very well. But it's something I've been thinking on for quite a while now. Because I love drawing Question Duck, and I've made it a rule to avoid danger, drama, or even pushing for great comedy. Creating something peaceful and serene yet keeping people coming back again and again, is an incredible challenge. I like to think I've had some small success in it. But I've always wondered just how long the legs are on its simple nature.