I've mentioned this before in other posts on this site, but I am a BIG believer in change ups, especially for my 10:U team. My son has developed one of the best change up I've ever seen. Again, it is deception because everything including his arm speed is the same as his fastball. The way he grips the ball requires him to throw it hard just to reach the plate. It starts about belt high and just falls off the table (no arc...or not much anyway). Last night the ball bounced in front of the plate and the batter swung. My other pitchers are starting to throw the CU and it's becoming all the rage (unfortunately, it is becoming too popular...they are throwing all the time and not setting it up). One of my pitchers who is 8 (league age 9) only throws his fastball about 38-40 mph (not bad for his age but a little on the slow side in 10:U competitive ball). However, he has developed a good change up and because of that he has disrupted the hitters timing that he is striking out good hitters with his fastball (or getting them to hit weak grounders). The CU is the great equalizer in my opinion.
Side note, my son and I were watching Roy Oswald pitch the other night and FOX kept showing his pitch speed...93,93,94. My 9 yr old son asked me why the pitcher isn't changing his speed to keep the hitters off balance! I love it!!