My youngest brother was 5 when mum died, I was 21 and there were several other kids of various ages between.
He probably accepted mums death easier than any of us, he accepted that she had died and was able to continue to function very well because he was so young. There were of course days when he missed her and asked for her but he adjusted very quickly.
We found the charity Winston's Widh to be wonderful, they have resources specifically to help children deal with bereavement, both before if it is expected, and after winstonswish.org/
What we have found as he grew up is that he has very few personal memories of our mum, he treasures any memories we are able to share with him, photos, videos, favourite stories, mementos, because he doesn't have his own to draw from.
He was 12 when Dad died, and that was harder for him. Because by then he was old enough to understand what death meant and he knew what he was losing.