Personally, I prefer to write adults. The only aspect of "being a kid" that I ever identified with... even as a child... is how intense "love" feels and how "important" the young among us think it is. I didn't watch Sailor Moon for the fanservice or because the cast was relatable (they weren't, and not because they were the opposite gender). I was watching it because I wanted to see Serena get together with Darian. I didn't watch Digimon because I related to the characters (okay, I related to Tai as an ideal to aspire towards), but I wanted to see all the cool monsters, unravel the mystery of the world, and see if Tai and Sora would get together or if Joe and Mimi would end up together.
As a child, I found it difficult to relate to children. I found it much easier to relate to adults. Or even, children who acted like adults. As a child, I never thought of things in the same way children in shows are portrayed as doing.
I think the most meaningful media I ever interacted with about children was "Ender's Game", in which the children in that story pretty much acted exactly as me and my friends did... and behaved the same way we had as children.
Children, by and large, don't "act like children". Children try their best to imitate adults. They try their best to imitate adult ideals, ideas, and responsibilities.
So, I'd rather write adults. I don't want to write someone who is hopelessly stupid like Spongebob in the delusion that "this is what children are like" (they're not, and they only act this way if they've been taught to or have some sort of mental deficiency) or someone who is doing their best to pretend to be an adult.
I'd rather just write adults. People with real problems that are spurred into action and out of their everyday mundane lives that they DESPERATELY want to get back to. I find that more interesting. As an adult, do they embrace the adventure and freedom of the situation... or do they just want to get back to what they're doing because... look... I got bills to pay... I got children to take care of... I'm putting my life at risk for something that is someone else's problem. Can't I just go home, make supper, and go to bed? I got work tomorrow and a mortgage to pay.