Over Christmas at my inlaws (that sounds pretty cold, we're actually quite friendly!), we went through some old boxes of things. Found in one of those boxes was an old toddler chair from when my husband was a, well, toddler. It has a TYKE-HIKE patch on the original seat. But doing a quick search just now shows that you can get the same chair from Hoohobbers.
The old seat was quite worn. It had been glued back together (perhaps a couple of times). I took the old seat off, made a pattern from it and then made a new seat with duck cloth.
Now its all clean, seatable, and ready for Keagan!