This is what my daughter made for her daddy for his birthday. It is actually a very nice thing to make even for younger kids. All you need are
-white or light coloured table ware that is oven proof
The porcelain colour comes either as a pen or in small glasses that you use with a paint brush. It simply depends on your or your kids' preference. We used a red pen for this project simply because we had it laying around from an older project. When my daughter was about 2 1/2 years old we used such pens to make cups to give away at christmas. Basically she scribbled with different colours on white cups. Too bad I did not take any photos back then of the results. I found them rather sweet. Now she can do already a bit more than just scribble. So she wrote "daddy" - in german of course - all around a huge cup and even drew a couple of hearts.
I liked the result so much that I told my daugher I would like her to make a cup for me, too. She responded that she could do that but I would only get if for my birthday. And I would have to tell daddy first where I bought the cup so he could go and buy one for me, too. She really had it all planned out ... ;-) (Now I only need to convince daddy ...)
It is really a nice project for kids. You simply draw something on the table ware. (You might want to protect the work surface as the pens sometimes splash around a bit.) As long as it is not baked you can also remove the paint again (just wipe it off) and redo bits. After you are done you let it sit for a while to dry and afterwards you bake it in your oven. DONE!
(If you are wondering - the brown bits on the inside of the cup are just coffee. I took the picture just after it was used for the first time and simply forgot to rinse it before. I was a bit worried that the writing would not survive the dishwasher since the pen had been laying around for quite some time. But after the first ride in the dishwasher the cup still looks fine!)