Re: My sims will not use the changing table in the sims 4.

I was having the same issue! I found the answer here: https://www.reddit.com/r/thesims/comments/1207fm7/comment/jdgacpm/?utm_source=share&utm_medium=web2x&context=3

Basically the babies in the bassinets are "newborns" but the table only works for "Infants". You have to age them up from Newborn to Infant before you can use any of the Growing Together items marked for "Infants". 
I just didn't want to take credit for the answer.