I am the Children's employee - hit send too soon -
Yes, bring a change of clothes and something comfortable to sleep in (yoga pants, sweatshirt, socks.) We are used to seeing parents in pjs.
The coffee bar in the lobby is decent. Better than cafeteria coffee and can make 'fancy drinks.'
There is a Walgreens onsite in the lobby. Ask for any discharge meds to be sent there so you can get them before you head home. They will even deliver them to the bedside. They also have a few snacks and flavored water down there too.
Bring comfy clothes for your kid to go home. PJs are fine.
Parking is a nightmare. It is $7/day to park, but you can buy $5 stickers at the Parking office.
http://childrensnational.org/choose-childrens/visiting-staying/transportation-parking. If you have to be here early for surgery, it shouldn't be a big deal though. It gets nuts later in the AM.
The hospital doesn't validate parking.
Good luck to you and your child!