Why are infants and toddlers nearly impossible to take care of?

Toddlers are ok just make sure they have enough toys to play with to build their skills and drag a plate of food from the fridge for them to eat from. This usually fulfils their needs. All adult sims need to do is potty train them until level 2 and bathe them. Infants are different and so much harder to manage they make toddlers seem so easy.