I started to doubt my information, so I got out the books. Couldn't find much in the Unofficial Guide, but I found this in a 2000 Birnbaum's:
Water Mouse boats can be rented at the GF, Poly, WL, Contem, Y&BC, FW, CB and DD marinas. When weather is warm, lines usually form about 11:00 a.m. and remain fairly constant until about 4:00 p.m. The minimum rental age is 12, except at Marketplace where the min is 14. Kids under the min may ride as passengers but are not allowed to drive.
At the Contemp marina, even zippier boats called Searaiders may be rented for about $37 per half hour. Accommodating up to three people, Searaiders can attain speeds up to 30 miles per hour; riders must be 18 to drive. Spincraft speedboats (slightly slower than Water Mouse boats may be rented at Coronado Springs (about $11 per half hour, $17 per hour). The min age to rent is 12.
Now don't forget this is from the 2000 edition of Birnbaum's so things may have changed. The Searaider may be something for me and the kids. I'm going to start a new thread to see if they are still around.