My friend has struggled with acne since his teen years. Now in his 40s, he will still get breakouts when under stress at work, which seems to be a new constant. He uses Clean & Clear with salicylic acid. I cannot use that stuff, I did once and my eyes swelled shut, my whole face was red, swollen, and burned. I have never struggled with acne but I needed something to wash my face with and I took some of his facial cleaner and it reacted poorly on me because I have sensitive skin. My ex would get boils on his back and acne around his neck. He would use Neutrogena's Oil Free Acne Wash. I don't know if your son is getting acne elsewhere, but that is an option.
By the way, my friend has like a concealer he dabs on to cover redness and scarring from acne. Maybe this is something that would help your son feel more comfortable if he has redness or pockmarks. I think it's also medicated, or it's non-comedogenic, at least. I think before doing all this though, I'd see a dermatologist. He could have a severe hormonal imbalance that will require more than just a facial cleanser. They also have stronger stuff (my friend in his horrid teen acne days would take a pill, for example) that your son may need.
As to your daughter, I would just get her some colored lip gloss in different shades. I had some light pink and dark pink ones, but I did not start wearing makeup at 12, I find that way too young. I was about 15-16. I actually was not interested in makeup but my mom thought I should start because other girls wore it and I was so awkward. She always said I was too pale so her thing was blush, and the colored lip gloss. I would get a Wet Shine Maybelline lip gloss, sometimes a glittery version of that, which they called "Diamonds" and put that on, she'd put the blush on, and that was it. I still use those colored lip glosses sometimes. I rarely use mascara, it seems to run if I blink and then I get raccoon eyes if I happen to also be sweating. You also have to be careful with mascara, it goes bad quickly and you can get pink eye from wearing mascara that is over 3 months old (been there, done that).