High chair is chaos! I think the parent taking toddler out of the chair, intends having them both sit down so the parent can ask the toddler if s/he wants food... They can't talk together while seated in the highchair. In a worst case the sim will assign seating on a different floor for that little chat, and you might wait for the toddler climb those stairs just to sit down to be asked if he is hungry, he says yes, and parent will carry him back to the floor with the highchair... argh... if you love watching a simday go wasted it can be fun watching. If not, it's veeeery annoying. The highchair usage is poorly designed, but even more annoying is that in TS4 sims don't always show their actions in that queue. If you tell a sim to feed toddler, the action icon might be "chat", and you are not able to see that the "feed" action is hiding until said chat has taken place. I have interrupted the feeding so many times just because I thought my sim had ignored my instructions.
Now I'm avoiding the highchair. Just drag and drop some plate into the toddler's inventory, and the toddler will eat it either on a living chair or on the floor.
PS: Re temperatures indoor, arriving a house might find sims freezing to death even in Summer. If you have not played the house in a long time, and the last time they appeared as NPC was in Winter, they might still have that temperature mood when you load them, but it fixes itself quickly. I never experienced it during a longer session in one house, only on arrival.