I hate the highchairs. Rarely use them. I just make a meal and then drag the food to where the toddler is and have them grab it. They eat the adult food.
I actually don't really my Sims to eat the quick meals too much. It doesn't fill them up as much and they have to eat more often because of it. All my Sims eat the normal food, I just try and give the toddlers the more kid friendly options. That'll get a negative moodlit sometimes if the food is a bit strange. They prefer the staples. I try to have at least one toddler friendly meal in my fridge at all times.
