Giving it another go...

I never mess with the high chair for this very reason. Usually what I do is have someone make a group meal. Depending on where the toddler is I will place the group meal on the floor or table and direct the toddler to grab a plate. Makes things a whole lot easier, especially if there are any stairs involved.

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.

The thermostat was the temperature issue, I didn't have one. Thanks for the advice on the high chair, avoiding them indefinately now!

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.

Nix the high chair.
It's useless. Just set out some food that the toddler can get to.
I also turned off temperature affecting sims in settings. If stuff doesn't work, get rid of it.

It’s frustrating, yes, but I find it kinda funny xD toddlers are my favourite, they deffinitely are challenging, kids and teenagers are kinda boring for me (I don’t have HSY yet). I have a lot of fun with toddlers and they are so cute. As for the high chair thing, I recommend cooking something for the whole family and leave it on the table and just click with toddler to get a plate, it’s much faster and easier. I know it shouldn’t be like that, it should be fixed but for the time being that is a good solution. As for the freezing, I think, if it’s not indeed a missing roof then it might be a seasons thing, in the fall and winter put the thermostat on higher level it should solve the problem. And if you just wanted to rant a little, I am here with you, my highchairs even have this weird glitch where when the toddler makes a mess and the chair is dirty I literally can’t clean it and everyone is tense around it and i have to sell it and buy a new one xD So no high chairs in my game for sure xD

I'm seriously thinking about trying an experiment. Some say we can still have the chicken nuggets without the high chair on the lot. I'll have to see if that's a fact. The other side of this experiment will be, if we do need the highchair for that kid-favorite meal, I'm going to see if I can have the highchair placed underneath the staircase, or if that won't work, in a basement/or attic.

On an aside, I believe a thermostat, if you have Seasons, should be added to the lot to help regulate hot and cold better. It's found under Electronics.

I think you can get chicken nuggets without a high chair. You do need a microwave to cook them.