really! To have the time and inclination to judge on it is one thing (really, aren't there more awful things to worry about?) but to comment on it while I can still hear them on a quiet street is well, just dim (not to mention rude) 
Yes, he is in a pushchair and yes he does look about 3 yrs old (he's not, he's 2.5 and tall) but we also have a two mile round trip to ds1's school over some incredibly busy roads. He can walk about half a mile at a fair pace but after that it becomes a snail's pace unless we are going to the park.
AIBU to have a little whinge about this? I certainly try not to go around judging automatically. And no, I wasn't brave enough to turn around and say all of the above. Not around here 