Need some advice on lighting a whole big room

Okay, I need some help/advice.

I'm pretty nervous about tomorrow. Tomorrow is my son's 3rd birthday party and I don't want to f up all the images with experimenting with a strobist kit. What I have for the party are this:

Manfrotto stand w/ a 36 inch white umbrella with reflective backing that I can take off - Mounted on to this will be my 430ex

Also have a 580exII that I will have on its stand pointing at the ceiling

Triggering both with an ST-E2 on my 5D.

The room where we are having this will be about 25 feet by 30 feet. I'm figuring that the umbrella should pretty much be pointed at the center of the room. The 580 shooting up to try and light up the whole room (was planning on cranking it to +2 or so).

Since there are going to be over a dozen 3 year olds at this party, I'm figuring that I'll pretty much be at f/8 the whole time.

Does this setup sound right to you guys?

As a parent of 2, I do understand the challenge of lighting the big room with lots of running kids. You have quite the challenge ahead of you.

Couple quick questions.

- How will you use the umbrella, reflective or shoot through? I would recommend reflective as it will give you a larger light source and more distance out of your light.
- Will you be using ratios on your lights? I would be careful not to use both at equal power or you might end up with really flat lighting.

I was planning on leaving the cover on and using reflective.

As for the lights, I was planning on having the 580 at +2 and leaving the 430 at 0

In a situation like this, I'd much rather do flash bouncing than setting up umbrellas with such young guests.... I don't think I want to have one of the umbrellas toppling over any of these dozen cuties running around....

The room is a gym like room for kids to tumble in. I was going to set up the light stand tied behind padding to a pillar, but I've decided to just go with bounce flash. It's something that I'm comfortable with and can predict the outcome.

And main reason for thinking of this setup is because one side of the room is a wall of windows. The sun beats in on the room, and from where I will be most of the time, the room will be heavily backlit. But if I use bounce off of the white card, or direct with a diffuser, I will be able to just use the 580 for fill.