kid's stuff 小儿科，儿戏

【例句】
This project is kid's stuff to me.
这个项目对我来说简直是小儿科。

Oh, now, Bill. You know how much I do. But over a phone? Now, really. That's kid stuff.
比尔，你知道我有多爱你。但是在电话里面？那是小孩子玩的把戏。