Sims 4 game wont let me create an infant child for my young adult mother in CAS

Hello. So, I have the new Growing Together pack and I'm not sure if I did something wrong but I have a young adult Sim that I want to create an infant as her child in CAS. But when I try to, it doesn't work saying " Must be younger than parents" while I'm positive that a young adult is older than an infant. I will attach a photo of what I'm trying to say. Thank you for understanding!