Parent pays for 1-to-1 coaching and now wants a specific position

I would keep the conversation centred on the child, not the money being spent. Private coaching does not buy a particular position in the team. The grassroots environment still has to make decisions based on the player’s development, enjoyment and the needs of the group. You can acknowledge that the extra work may be useful without agreeing that it has to be “used” on Sunday in one role. I would also check what the child actually wants, because adults can build a pathway around them that they never asked for. Explain your approach to rotating roles and what you are trying to help the player experience. There is no need to criticise the 1-to-1 coach. You are simply making clear that two environments can have different purposes.