I'm pretty sure that any of them can be sprayed down and wiped for decontamination. I can't imagine any of the companies putting one out that is difficult to clean.

The main advice I'd give you is to speak to somebody at your local EMS service, and let them know what you want to do. They might have a specific model they want because of their existing equipment or protocols. They will also probably have better negotiated prices with vendors than what you pay retail. They might also have requirements that all squads must be equipped similarly, or that any new equipment has to go through an overly long approval process, with training for all EMT's.

The easiest thing for you to do is approach their supply or operations officer, and tell them your story, tell them you would like to donate child immobilization equipment (or any other PEDs equipment they desperately need), and cut them a check.

EDIT: My perspective on this is from running a small EMS agency that worked with volunteers and did not charge patients. We managed to provide an sub-2 minute response time average on our college campus, with very well trained providers, on a shoestring budget. While child sized immobilization equipment is a nice thing to have, a good provider can make do with blanket rolls and careful strap application on adult-sized backboards. I would first ask if there is any vital pediatric equipment that is higher priority for them. This would include such things as child-sized resuscitation equipment, pediatric-dosed auto-injectors (if they use them), pediatric defib pads, and any other life-saving devices.

Another great thing for an ambulance to have is small stuffed animals and soft toys that can be given to a child to calm and comfort them in an emergency situation. I hit up the thrift stores near me a couple times a year, buy a whole bunch of toys, clean them, and leave them at my local fire station. It's amazing how well a new toy works to comfort, and most importantly distract a small child who is hurt or sick or whose parent is in a bad situation.