Sadly it's what many people think, that's why I don't really tell a lot of people I watch anime, (especially how much lol). It's not really accepted where I'm from.
But I always think when I hear people say that it's for little kids, that most the アニメ i've seen I wouldn't want kids to see. I think there are もっと見る serious animes out there than not.... または at least I guess those are the ones I stick to. No.6, Wolfs Rain, Another, Code Geass, and Psychic Detective Yakumo are just a few of those animes that take there audience very seriously.
To be honest I've never actually heard anyone say that...
But some shows are for kids and if someone wanted to think that, it's fine it wouldn't really bother me. If they're saying something like that they probably don't watch much アニメ anyways so it doesn't really matter.
those people literally don't know anything. It's like saying "oh it's a comedy movie Adam Sandler is definitely starring in it." Like typically the only アニメ I can think of that's purely for kids is Pokemon.
When ever someone says アニメ is for kids I look at them and say..Can アニメ make あなた cry..does アニメ have porn..does アニメ has romance..does アニメ cuss..does アニメ scare people, yes it does and Im sitting here like now あなた know :L