Just go with it mate...it happened to me with my son, he was 6 at the time he is now coming to the end of U14s and has just been given another 2years taking him to the end of U16s
Go with it and let your son enjoy it, take each 6 weeks as they come,
It doesn't stop him supporting the blues we are both season ticket holders, just take it for what it is quality coaching and training and if he does get a chance to sign for them at U9 and stay with them the experiences he will get playing in different countries etc are well worth it, my son has played all over Europe in tournaments and is of to Holland again at the end of the month having just got back from Turkey last month
So let your boy enjoy it but take it for what it is extra training and keep your feet on the ground and take it one step at a time, also if Utd have expressed an interest you can be sure other clubs will, my lad was scouted by City too at the time but didn't enjoy it when he went which broke my heart, but i couldnt force him you have to take them were there comfortable
So bear that in mind, good luck and go with the flow who knows where it could end