|I still love this story!
A few suggestions, and they focus mostly on tightening up the prose.
1. Avoid the use of "which." For example:
Whenever I think of Christmas there is one in particular which stands out in my memory.
Try something like Whenever I think of Christmas one stands out above all others in my memory.
2. Lengthy sentences:
Two uncles, three aunts and all their assorted families from my father's side and three aunts and three uncles and all their families from my mom's side. That was a total of eleven spouses and about twenty five kids, not to mention mom, dad, me and my brother and my grandmother...mom's mother, all of them converging on the house Christmas eve and all were spending the night so they could enjoy the whole of Christmas day together with us.
This could be clarified by adding a few commas as well as separating it into more sentences:
Two uncles, three aunts, and all their assorted families from my father's side, and three aunts, three uncles and all their families from my mom's side. That totaled eleven spouses and twenty five kids. Plus (eliminate 'not to mention' because you do mention them) Mom, Dad, me, my brother, and my grandmother (Mom's mother), all of them converged on the house Christmas eve. All spent the night so they could enjoy the whole of Christmas day together with us.
I made a few other modifications such eliminating passive verbs like "was" and "were." By replacing passive verbs, not only will the story become more active, but the sentences will tighten up.
3. Watch those adverbs:
"Get up, sleepyhead," he said softly.
Simplify to "Get up, sleepyhead," he whispered.
These are only a few examples and recommendations. I suggest you read it out loud either to yourself or someone else. Sometimes reading out loud can tell you best if something needs to be shortened or reworded for better flow.
You tell a beautiful story, and you write in a conversational tone that is quite appealing. I don't doubt this will be published.