Infants milestones

I've been playing with multiple infants in my current legacy challenge and the past three generations the infant milestones are not progressing at all. My sims spend hours with the infant on the playmat, the whole household stop whatever they are doing to watch milestone, but nothing is happening and it doesn't appear on the infants' simology panel. Very frustrating. Please fix as I don't see other players reporting it I don't know if it is an issue.