Does anything like this exist for TS3? Or, if not, can anybody recommend a custom costume makeup than I could repurpose as sunscreen by playing around with the colour wheel?

The Island Paradise EP has sunscreen makeup exactly like that.

Oh my goodness, you're right! I just checked and it.s right there. What a clown. No idea how I missed that, maybe I saw it wasn't there for toddlers and forgot to check for everybody else. It's a shame it's not enabled for the tiny ones but this is certainly better than not having it at all.

Thanks for taking the time to point this out to me haha, who knows how long it would have taken me to realise on my own.