Cleared for take off is a blind faith trust from the pilot to tower. I have no idea if someone is about to land on the opposite end of the runway I am taking off from.
Also there is the uncertainty issue. The pilot doesn't really know who he's talking to, only that they are talking on tower frequency, which anyone with a $200 hand held Av band can do. Adding a kid's voice is so unusual, I can see it raising some concern to a pilot .
All in all a very bad idea. The landing/takeoff phase is no place for cuteness.