I love Tankas..I love your poem..!!
I love the twist @ sorrow and laughter..I love the feelings and impressions that I felt..well done..

I remember best
when we were young children
Your laughter.
^^actually you need the semicolon after children..not after "How easy it came"

How easy it came; how infectious it was.
^^
because here you should add a comma.. OR take off how infectious it was and say:

How easy it came; infectiously
^^then it works that way :)..or else grammatically it's wrong to place the semicolon there... (it's what I ALWAYS do :( sadly)

And that it thrilled me and everyone around us.

^
however..this stanza is absolutely breathtaking..I feel your passion..and it reflects something very special about your personality to be able to focus on these sweet details..show that you are either sensitive or..loving..caring..or romantic..or all of them :).
Great wording! as well

You were always
as quick to laughter as to sorrow{add a comma}
But now
^^you don't have to capitalize B in but..sounds weird..

I have heard your laughter for the last time.
I still won't acknowledge that you are gone.
^^
anyway mind these details..you almost had me chilled..this stanza and this ending is fabulously piercing and they bit me in a way and another..

a great poem...looks forward to see more..
you are a great "talent"5/5