He didn't Accept it, He thought it was a joke and Voldemort was his dad, Also he couldn't remember it.

For Quirrel's death he blacked out before he died

I’m just gonna copy and paste what I told another user a few minutes ago when hey asked this and if you have further questions I’ll be happy to answer:

it’s because he was very young and don’t understand their deaths well/at all at the time when it happened nor was he able to accept the death mentally really. Ofc he was able to understand their deaths later on in life and he understood it’s better later on, but as 1 year old baby, he had no understanding of what was happening, so it didn’t really count much u til the death of Cedric, where he could understand it and freshly grieve over it.

Oh, that makes sense! Thank youu. :)