I feel your pain!!!
I do home daycare and we put in a vessel sink in the lower level bath..where my daycare area is! Kids need to be up high so they don't "hang" on the glass bowl when washing hands, etc.
I have this one. Its called an "EZ FOLDZ" its 12 inches tall..and really any taller and my kids would have a hard time getting on and off of it. I have never brought it up to the kitchen?? I should try that. I could use a better system up there, but mostly I make them wash in the bathroom before coming up to the table.
I have one just like it that is a smaller overall size (but still too tall for potty use...great for handwashing in my other bathroom). The lovely thing is they fold up under a sink or next to a toilet in my case, for easy storage.
http://www.amazon.com/Plastics-104-6WH-White-Foldz-Stool/...
I have a black one in both the 12 inch tall one and the 9 inch tall one.
I paid about $30 for the 12 inch tall at Bed Bath and Beyond (online only) and $15 for the 9 inch..can't remember where I got that one, but it is more readily available. I love the big one as it has a large top surface as well. We use it all around the house on the weekends...it can support up to 300 pounds. My in laws got one for a step stool for Hubbys elderly Gramma to get up into my Father in Laws pick up truck. All kinds of uses..but I got mine mainly for daycare handwashing uses!
Hope it helps! I love these things and wish I had found them years ago!