My DD who is 4 can do dots, I'm sure a 12yo can do one thing better - help do the dishes when they're done
O.k. since it's family, no biggie on having the kiddo in the kitchen. You teach her just like you'd teach an employee first starting out in cake decorating, teach the fundamentals of "WASH YOUR HANDS!!!
", tie your hair back, cover it with a net/hat, and nail them on it every flipp'n time they touch their hands to their face or pockets...
It's the old story of "teach a person to fish vs. catching the fish for them..." A 12yo isn't going to produce something that's fancy schmancy perfect, but you know what, it's the perfect age for them to pick up a piping bag and do carpal tunnel stars for a Wilton pan design. I've still got the picture of me holding my own Holly Hobby b-day cake around that age (fro - aka WAY too tight of a perm - and all too I might add!). At the time I thought the cake was perfect, now I look at it and go "and I thought THAT was presentable????" LOL
This is an opportunity for her to learn, she's old enough to do the full cake by herself (remember baking cakes for the fair at age 8!), the idea being that the Mom hasn't a clue or the materials to do it herself, the 12yo wants to do it, and you've got the supplies/equipment but most of all the skill... You're just there to supervise, possibly mix the icing colors to proper levels, and teach her how to do carpal tunnel stars, nothing more, nothing less. She's not a baby, she's a young woman, heck, I had my first job at 11 washing dishes for a restaurant and that was two years after I became the cook at home during the summer... Now, put a piping bag in her hand and tell her "go to town". It's a chance to teach her a life skill, not everything comes out perfect, and sometimes it just doesn't matter, the only details that matter is that she did it, and it tastes good.