Lol. Sounds like the sims to me XD
I agree with the other posters about high chairs. They are cute but not worth the hassle. If you do want to use them, they seem to work best when the toddler asks the parent for food.
If you're getting back into the game after a long time, a small house is easiest.
For the temperature, changing into warmer clothes should have fixed it. As long as you did that by choosing the toddler's Cold Weather outfit, not just altering the Everyday outfit to something that looks warmer. You might have to wait a few minutes for the tot to warm up.
For the thermostat you only need one per lot, location on the lot doesn't matter.