I've tried this two different ways:

* I'll put the kids down one at a time (my older kid keeps wandering into the room I'm in with my younger kid though).
* I'll put them both down at the same time (but then if the kids aren't tired, they will make each other giggle and stay up for a long time)

I can usually put them both down, but it delays bedtime by an hour or more. I've had the most luck when we all sleep in the same room, but I don't like to set that precedent!

Last night I totally failed to get them both down by myself though. I think I'm doing it wrong... would love some tips and pointers!