Go ahead, it's well worth while.
Long ago I painted a set of outdoor tiles for Truro City Council (all the Cornish wild-flowers so the public could identify them) but they had to be fired, so were loose.
In 2000, I was commissioned to paint the children and domestic animals of the family, on kitchen tiles, in situ for a local farmer.
I can't remember now what I used but I did coat them (the tiles not the kids
) with clear polyurethane varnish for extra protection. They're still going strong after multiple cleanings. No firing was needed of course.
Are you an experienced painter? If not, find a design you like and copy it.
Will you need to stand, sit, bend or lean in an awkward position in order to get at them? If so, put a time limit (15 mins) on how long you work and take frequent breaks, or you'll have aches on your aches 
If you decide it's too daunting a task, and I hope you don't, there's an alternative. Using postcards, wrapping paper, art prints or whatever takes you fancy, cut to size, glue them onto the tiles (don't use PVA glue) and give them several coats (6-7 over the same number of days) of polyurethane varnish to protect from steam, grease etc.
I did this, though not on tiles, with a full set of Flower Fairy postcards, which my first grand-daughter wanted on her bedroom door.
Good luck and ENJOY!