Reps with distractions around the fielder.

On a deep kickoff return, the returner should be fielding the ball when the coverage team is at least 15-20 yards away from him (further if it's a legitimately deep kick ... i.e. beyond the 20-yard line, in which case they'll be 20-40 yards away), so there is absolutely no reason to take your eyes off the ball to field the kick.  In my experience, the biggest problem youth kick returners have is that they want to run horizontally in an ill-advised attempt to line up their blocks.  Unfortunately, this method can work against poorer, undisciplined teams, so it's easy for your returner to get positive reinforcement for doing things incorrectly.  Likewise, one of my major pet peeves is lead blockers stopping to line up blocks only to have the returner run by them and have the defender they were trying to line up make the tackle.  You have to teach your returner to get going vertical full speed as quickly as possible - splitting defenders before they have an opportunity to converge is your best bet for a big return.  Likewise, you have to teach your KOR blockers to get in front of the ball and then turn towards the opposition, pick out someone to block and then go after them aggressively.  In my experience, the best way to develop this aggressiveness is to tell them in advance who they should be going after (i.e. #2 from the sideline or #3 from the sideline, so they know which player to keep an eye on).  If you can get your return team to attack the coverage team aggressively and get going full speed vertically as quickly as possible, you will rarely start an offensive series after a kickoff any further back than your own 40 (really, failure to field the ball cleanly will be only reason for poor field position.

Any tips for deep returners?

We had two bounce off our deep guy's knee.

On the fly, or short hop?