The only reason I thought of putting the child on the aisle was because from the OP's original post the comment "will she be isolated from us" indicated to me the parents wanted to take two seats together, with the child on another row of two seats.

By suggesting the middle seats, it meant that if (as I believed) the parents wanted to sit side by side they could, whilst at the same time they didn't have to have their daughter in another row.

I wholeheartedly agree that it would be better to have the child in the centre with one parent whilst the other sits on the aisle, but I was trying to help in what I thought they actually wanted to do.