Responses
I think like future kageyama said the baby is an accident & at the end we see the younger members being confused as to why they were all gathered there so they lost their memory of meeting the babies hence why future kagehina as no memory of meeting their kid when they were young
Just to let myself understand what happened
It's basically a time paradox(?)
If the past kagehina did not pick up the blanket, they wouldn't have found the baby and kept it safe and they wouldn't have met the future kagehina who were the parents of the baby that traveled through the blanket portal and lastly they wouldn't have thought of having the baby resulting to a loop where I don't clearly see where it started...and my brain is cooked