Going to jump in here because I see a lot of people insinuating it’s not American to invite the entire family. I’m an American and if I was dating someone for 2 years I would definitely do one of the 2: - invite my SO and their kid to the birthday party (as well as any close familial relations, birthday-haver can choose the rest of the guests) - OR separately have a family celebration as well, perhaps we go out to eat or gather for cake and pizza at home as a family group (would invite my SO and their kid to this if birthday-haver is at an age where they are choosing all guests for their big party)

As kids, we’d often to the second one. Have cake, food, and gifts to celebrate with my grandparents, parents, siblings, aunt, uncle, first cousin. My first cousin would sometimes invite the cousins on her other side to this too and we’d all celebrate together. Then we’d have a friend birthday party too.