Fwiw, your kid is U11, so playing 9v9? he just finished playing 2 years of 7v7? If he hates it, then you should leave. That said, you should ask the coach what position he sees your kid playing when he gets to 11v11.
One of my kids played CB in 9v9, which was weird because he wasn't the biggest or strongest and didn't want to play there. We spoke to the coach about 11v11 (i.e. what is he developing the kid to play in) and he said that he saw my kid as a MF, probably 6 (CDM) and he wanted him to develop defensively plus he trusted him there as he could play the ball on the ground, read the game and organize the team. As he said, a CB at 9v9 is more like a 6 in 11v11 - field size etc. At 11v11, he has played every position 6-11, but never played as a defender (under multiple coaches club & HS).