I did not aim to imply (and it certainly wasn't intended as an excuse) playing multiple sports caused my son not to go to State. He had opportunities to train in between seasons, but everyone needs some time off.
The two wrestlers on our team that went to state "got it" from an early age. They had natural mat sense and strength. They both benefited by wrestling tough competition during the Spring, which afforded them the opportunity to wrestle national competition with Team indiana. The increased mat time, their natural ability, and their training partners were key to their success. One of the two had less work ethic, but he had the most mat sense and natural strength.
My son played Soccer (because we don't have football) and he played baseball. While Soccer certainly contributes to conditioning neither sport really helped with wrestling strength, but again he was happy doing what he did.
My son did beat two kids, at team regional, who ended up placing at state, so to say he wasn't good or didn't do well because he played multiple sports is certainly far from the truth. Could he have done better with some more mat time and time in the weight room? Most likely.
The key to building a program is to start young. You may lose some kids when they get into high school, but that is just part of it. This will take time and effort from parents, coaches and kids, but the rewards will be worth it. Certainly don't worry about a kid playing multiple sports (unless it is basketball!).
I talked to a coach from a 2A school yesterday. Their team won the tournament we were at and they have consistently been a pretty good team year over year. Their school has football, so I asked him if football was key to their success. He said no that in fact the wrestling team helped the football team more than the other way around. He has a person on his staff that is also involved with football, so they are trying to turn it around. I also asked him about their youth program and he said they don't really have one. He said he lets the 3rd, 4th and 5th graders hang out with the Junior High team. He stated that he was willing to take kids to tournaments, but the kids had to ask for it. Somehow this works for him. He has a full team plus 10 or more reserves. He has been at the school for a long time and he does teach, so I would say that is a pretty big part of it.