I can see why you wouldn't want to - it's the regular tie and if you end up with one of the kids off sick or other people staying or want to be away or do something different - well you can't or feel obliged to stop and sort out their child. or if they are running late and you then end up late or or you want to leave early but can't because you are committed to waiting for them. Or what if the children suddenly fall out and you have to deal with WW3 between them for several weeks?
If your house is anything like ours, those last 15 mins before getting into the car are often the most hectic of the day, trying to chivvy little ones to brush teeth/get shoes on/make sure packed lunches get in the right bags, everybody has everything and that nothing that has already been put out to go disappears before it gets in the car etc etc.
To have somebody coming at that time would throw a real spanner in the works as you would have to stop what you were doing, take child, listen to any handover stuff they wanted you to know about, and potentially settle the child if it was upset or just so he didn't get upset with everyone rushing around him. then you would have to finish doing whatever you were doing, and it is always dangerous when you are interrupted in the middle of doing something, that is when you are most likely to end up not finishing it or getting it wrong.
Plus it is going to take longer to drop off 2 little boys at school as they need longer helping to go in, putting bits away, handing over etc, it's not like a ten yr old that you can just drop at the gate and wave goodbye to.
Maybe offer to take him if they have an emergency but not on a regular basis? Thing is, I know that it is nice for them if they don't have to fork out for a breakfast club and that their ds gets to play with his friend. But unfortunately that is why breakfast club exists - because they do have to be away before school starts and because it is a big imposition for someone else to have to take them.
And a bottle of wine is a bit cheeky - whilst it gets around the embarrassment of discussing money say they drop him off and he is at your house for 15 mins before you go plus it takes 15 mins to get to school and drop him off plus you need to be ready extra early that's well over an hour a week of your time, probably for a bottle that was bought on a 3 for £10 (ok that's a wild supposition
) Wonder if they would want to look after your child at a really busy inconvenient time for an hour for a bottle of wine?
Could you remind them of that legislation that was going to make it illegal for anyone to do any sort of childminding on a regular basis without them being registered etc? There were the policewomen that were done for looking after each other's kids on their days off as they were getting something for it (ie free childcare) even though it wasn't money. Think that then could have led to them realising the legislation was a bit over zealous and was going to be toned down but you could still be worried about it
if you needed to be!
Definitely think you need to think of your family here and the extra stress it will cause and say that you are sorry but it's not possible on a regular basis (and remember to not give them any reasons so they don't think that they can 'fix' the reason and then you will be able to do it...)