No Nick, the government did not interfere, an individual Ofsted inspector did, Oftsted were told that they shouldn't do that and they mustn't do it again.
You correctly identify that giving meat in exchange for childcare would be reward; and would therefore be regulated childcare (if it met the other criteria). That is why Ed Balls' letter refers specifically and only to reciprocal child care, ie looking after each others children, not anything else.
You are coming at this from the wrong end Nick. According to your cautious view of the world, my 6 year old son can't have his friends round to play because I am not a childminder. That is clearly nonsense, so where do you think the line should be drawn? It has to be drawn somewhere, and Ofsted have been told that it needs to be drawn the other side of reciprocal childcare.
You won't find anything on OPSI because there has been no amendment to the statute, but Nick you need to understand that there is more to the law than what is written in statute. According to the the Easter Act 1928, Easter Sunday is 10 April 2010 in England, but this law is not enforced because it would not be in the public interest to enforce it. You could say the same is true of much of the current governments legislation, but as far as reciprocal child care is concerned the government has made its position clear.
Changing its mind in future? And do what, get Ofsted to issue enforcement notices against people for doing what the govermnent had said they could do? No right-minded court would uphold such an action, and fortunately the independence of the courts in England and Wales (and elsewhere in the UK, but that is not relevant here) ensures that they are, at least to this extent, of the right mind.
Nick, in this case the people have won and the nanny state has lost. It would be a tragedy if we were to be so subserviant as to act as though we had lost regardless!