Sign the kids when they are in 7th grade to go to school at a prep school that the college owns so that when they are freshmen, they have the system down pat.

Once a player signs with a college, they are there for 4 years, no transfers unless a fee is paid, and there are no redshirt seasons. Player sits out a year due to injury, and they get a 5th year, that player is a free agent.

Players can't leave for the NFL until after their 4 years are up.

With those things in place, there will need to be one more thing, a Collective Bargaining Agreement. Monopoly and Anti-trust laws are different in the US and Europe. To be able to control player movement like this, a CBA would need to be in place. At that point, the players become employees of the college, and if that college is public, a lot of states have laws against state employees being in unions, and a lot of states are "right to work" states which say union membership is not mandatory.