I'm white (which I think is relevant) and tbh if I saw the advert with a white and black child wearing that top, I probably wouldn't give it a second thought. I call my dd a monkey, I just call children monkeys sometimes, meaning like cheeky/naughty.
But due to the historic (and sadly, still present) usage of monkey as an insult to black people, I imagine that some black people who've experienced being called a monkey in this negative way will make a link immediately and be upset by it. I don't think I'd say the advert itself is racist as it obviously using monkey in the way I would when calling my dd a little monkey etc, but maybe thoughtless/ socially ignorant or something like that? And really, given that their job is to advertise they should be more aware of their audience. I mean I am assuming here that most people involved in the making of this advert were not black, but I suppose there could have been black people involved who were not bothered by it or scared of speaking out if they were.
I think my overall feeling is that this is something that should not even raise eyebrows in an ideal world, but we can't ignore the fact that the word monkey has been, and is, used in a racist way...in an ideal world this wouldn't be the case and we'd have no problem but we can't ignore reality.
This has made me think though, would it be wrong of me to call a black child a cheeky monkey or something? I'd never mean it in a racist way, but perhaps I might unintentionally upset or offend. But I also don't like the idea that I'd be treating a black child differently to a white child by going out of my way to not call them something, if you see what I mean.