Hi there,
I recently succumbed to a very tempting info-mercial on the Swivel Sweeper, for this very reason. I was constantly on my hands and knees wiping up food particles under the high chair and in the kitchen. Yuck! Sweeping was gross, and the swiffer duster still required me bending down to sweep up the particles. I had to have a better solution, so I broke down and ordered the Swivel Sweeper online. www.swivelsweeper.com. It's not much larger than the head of a Swiffer duster, but it's battery operated, and picks up almost anything. I just wait a little while after dinner (i.e. after bath and bedtime) to allow the food under the high chair to dry. Then I swivel-sweep up the crumbs. I don't use a mat under the high chair cuz it's just easier to clean up the hard wood floors under the high chair. If you have carpet, I'm not sure it would work as well, but it still may vaccuum up the crumbs directly off your vinyl mat. I love this little device! It ended up being about $35 (actually $70 for two of them, and I shared one with a friend and we split the cost!). Well worth it! Good luck solving your mess problem--you're not alone!
A.