I think that sounds a little small.. but then it depends on the size of the kids. I just finished 2 aprons for my great nieces. The oldest is 6 and younger is almost 3.. The bigger one is 23" from top to bottom and I am sure the bottom was close to 18" wide The smaller one was about 19" from top to bottom. But I made them big so there would be room to grow into them
I would second the suggestions you received. If you can sew ruffles on them that would be very cute. My sis used the tape measure to get me a good idea on size
Good luck!