OMG my ds1 is at 4yr kindy too. And we do what you do, I have a toddler seat on the pram in case he gets tired from walking but I also encourage him to walk. I also offer him something to eat as soon as i have picked him up as he is always hungry after kindy even though he has fruit and a sandwich there. If his TA made comments like that to me I would be furious. She is exactly that, an aid not the teacher. I would ask to have a meeting with the teacher and the principal as she is way out of line.