Comfort them as best as you can. Do all the things you usually do since you are best friends anyway.Don't force them to talk about it, and don't bring it up, but if they want to talk about it or they bring it up, Just listen and comfort them with hugs. If they seem overly down, try to cheer them up/distract them with things such as play dates, movies, and sleep overs at your house. Most of all, do not treat them any differently or it will make them uncomfortable and they will feel awkward.