I don't know if this has been posted, or discussed, however I just found this on the pedipeds site, and hopefully it'll be helpful! I have no idea what size Ty should really be wearing, and we don't have a Stride Rite convenient to us, or really any kids shoe place that I'm aware of, so this is the next best thing!
https://www.pediped.com/Files/content/ShoeSizingChart_Oct2011.pdf
Re: Another Shoe size post (downloadable sizing chart)