It's very true that we will always hold dear to our hearts our beloved little ones that have passed away. I also get the nostalgic feeling and the longing/missing more during the important dates such as their hatchdays/homecoming days and the anniversaries of their passing.
May your Billy and Bertie continue to rest in peace.
RIP sweet Tito (Summer 2008 - January 17th 2013).
You are missed and never will be forgotten.