THe way that we have done it is--if an elderly, pregnant, or mom with small child enters the bus, DH or I and DS (who just turned 12 and is already 5'7") get up and offer their seats. I have let DD when she was younger and weighed less sit in my lap. I do not let DD give up her seat b/c she can't reach the overhead bar. Now that I have a younger one --DH or I will have a seat at all times for him. IF there aren't any seats we will not ride.