My co-grandmother died just over 2 years ago. Our shared GC, both boys, were just 8 and just 4. They were saddened but not distraught. The older boy asked to go to the funeral and this was, eventually after a lot of heart-searching, granted. He cried, along with everyone else, but I think that helped him understand and come to terms with losing 'grandma'.
The younger boy talked about her more, at least to me. He asked if I could please be his 'grandma' now. This confused me as I was always 'nana'. He tried to explain that now that grandma had gone he'd like me to be both 'grandma' and 'nana'. I wasn't sure how his mind was working on this but I agreed to be both and that made him happy.
They both occasionally talk about 'grandma' in terms of affection, so she's not forgotten.
I'll be thinking of you today NanKate 