Sydney Sweeneyand Scooter Braun made a smooth smoothie run with his kids … hitting up a local shop in Los Angeles a few days after they touched down in the City of Angels.

The actress and music mogul took two of his three kids to get a sweet treat Tuesday afternoon … and Sydney looked super comfortable chatting with the little ones when Scooter was busy ordering.

In fact, she even slung an arm over one of Scooter’s sons’ shoulders … walking casually through the parking lot in her white T-shirt and blue jeans. Scooter embraced the California beach bum vibe in a pair of shorts, a T-shirt, and a cap.

The kids dressed more uniformly … and we mean that literally because it looks like these two just got out of school and are still wearing their academic garb.

As you know … we saw Sydney out with Scooter and his kids for the first time last month — with the group hopping off a private jet together at Van Nuys Airport in Los Angeles.

All three of Scooter’s children — Jagger, Levi, and Hart — were present on that flight … and, again, it was notable how at ease Sydney seemed around them all.