The best family games like Super Mario Galaxy are Super Mario Galaxy 2, Super Mario Odyssey and Astro Bot. Below are 9, each with the reason it is here — and, at the end, what filtering to family costs you.
Filtering to family means the game has to work for a child and an adult at the same table without either of them being bored. That is a much harder design problem than a difficulty slider.
What you get: Something you can put in front of anyone. The best family games make the skill gap not matter rather than pretending it is not there.
What made Super Mario Galaxy worth playing in the first place is covered on the full list. This page is the family part of that answer, and only the family part.
More of it, denser, and with Yoshi. Arguably the better game.
The successor, with a deeper moveset and less structure.
The only recent platformer with as many ideas per hour.
The same one-idea-per-level discipline, in four-player co-op.
The best indie take on this era of 3D platforming.
Every level a new concept, executed properly.
3D platforming built to be kind and full of small inventions.
The origin, and the moveset is still the deepest part.
Galaxy's diorama levels turned into a whole puzzle game.
Edge. Family games rarely go anywhere uncomfortable, and a few of them are too generous to hold an experienced player for long alone.
The full list is on games like Super Mario Galaxy — 9 picks, no genre filter.
Super Mario Galaxy 2. More of it, denser, and with Yoshi. Arguably the better game.
No. Super Mario Galaxy released on the Nintendo Wii, but a recommendation is only useful if you can play it, so the picks above span platforms and eras. What they share is the genre and the reason.
Age ratings cover content but not difficulty or frustration, which is what actually ruins a family session. Five minutes of unedited play footage tells you more than any rating.
With mixed ages, co-operative usually wins. The competitive ones that work are the ones where being in last place is still entertaining.
By hand. Each pick was written for the full Super Mario Galaxy list first, on what the game actually does, and this page is the part of that list that is family — never a genre tag lookup, which is how "best racing games like Super Mario 64" used to be a page on this site.
Or read the family guide for where to start in the genre generally.