A nice place to eat lunch on my wife's birthday (20th of july) with a 3 yo kid?

We're a danish couple coming to Berlin for a week soon. During our stay, my wife has her birthday. For dinner we're gonna eat at our air BnB because our son needs to go to be early, so I want to find a nice place for us to eat lunch. We do need to be able to bring our 3 yo son but he is quite welbehaved.

Other activities for the rest of the day is also very welcome.

Thank you in advance from your neighbor up north.