I also noticed that you can feed toddlers in the high chair with their special meals (cereal, applesauce, ham sandwich etc) even with the Simple Living challenge turned on. Technically I think you should only be able to give them food from your sim's inventory. I am guessing they forgot about the high chair as well, or else they didn't want any starving toddlers. To tell the truth, I was actually relieved by this because I had moved my family into their Simple Living House in Cottage Living late at night and they were all really hungry. However, at least they could feed their toddler and put her to bed, before ordering their groceries and Zoomer's delivery.