It's policy here that children in kindergarten cannot be unattended at the stops, wether pick up or drop off. They will not even let the child get off the bus if you are not right there at drop off. Maybe there is a similar policy in place and thats why the bus driver gave you "the look". I would make sure, the last thing you need is to be reported by some nazi driver. If not then good for him for being such a big boy! And I would just smile and wave at the looks next time, lol.