In the scene where Todd Bowman is riding his bicycle to Dussander's home (I believe it was for his first session with him), we get a close up of him riding the bike...and more importantly (at least for the purposes of this slip up) we see he is wearing sneakers. Next shot is him pulling up in front of the house on the bike, and then going up the stairs to the porch. If you look, his shoes have changed into some kind of leather shoe!