Had a few kids coming home with us for playdates recently and I flatly refuse to carry anyone's bag. It's caused some upset from them and one of their mums commented on my 'tough love' attitude...
My kids love an effing huge Smiggle backpack filled with god knows what toot but I make them cart it back and forth. They want it, they carry it is my rule. The kids that come keep just HANDING me their bags as they exit the school and one huffed all the way home whining that it's SOOOO FAR and MY BAG IS SOOOO HEAVY and YOUR MAMA IS MEAN (that one demanded the WiFi code as soon as she got in) 
It's a 10 minute walk max. With a backpack or a book bag. my DC's/their mates are 7 &9 I'm not a bloody mule... AIBU? What does everyone else do?