Wow - £5 per day? I find that a bit greedy. I thought you were going to say £10 a week. Or a couple of £ a day.
I've been sitting nodding at all the posts saying you're doing them a BIG favour by childminding.
OP - you keep on saying that looking after DD isn't an inconvenience. As if to say that cancels the give and take side of the lift for your DH.
Well surely the fact that this guy is going to be doing the same journey weather your DH is in the car or not means that too is not an inconvenience either? (If your DH is late/other bloke is late/whatever, your DH can get a bus, so it's not that heavy a responsibility for him)
And yet you're willing to pay. ANd most people reading this would be willing to pay. I'd bet most people reading this would have wanted to give you some token of appreciation re: the child care you do for them by now too.
Personally i wouldn't want to have any confrontation about it either. Let DH pay, but from now on say no to the unpaid, unappreciated childminding. You'll fester otherwise.
If they want their rightful dues for the driving but are unwilling to reciprocate when it comes to childminding - just take a step back, don't do it for them any more, and try to forget about it.
Some people are not good at give and take, best not to expect it.