BIG decorator here!
I also try to avoid themes but it's good to pick some overall style that you want to work from (classical, girly, contemporary, etc). Again, think of a style, not a theme. Do you have window treatments picked out yet? If you could post a pic of the bedding and maybe even the room that would be fantastic, now then I could give you some ideas. For wall color, try picking out a "supporting" color from the quilt. I usually like to pick the third color in order from how frequently it is used, but I would just choose your favorite. Go to Home Depot or wherever you plan on buying your paint and get some chips of a few colors in it, then bring them home to see what you like.
For accessories, try going to a TJ Maxx/Home Goods (discount home furnishings, pardon me I have no idea what stores you have in OK) type place and see what they have for trinkets. They usually have some art and little tables that you can incorporate, just don't go to the point of tacky like my DH does.

Try looking at Poshtots.com for some ideas.
Do have chairs or tables or anything already? It's nice to get a big chair/loveseat to curl up in, you could take one from somewhere else in the house and put a slipcover over it if you're worried about cost (of course it you're not that changes everything

). Do you have a playroom or anything like that, or will these be their main "play place" other than the living area? Is there anything special like an activitytable that you would like to incorporate? This type of info should help me generate some ideas.
For your DS, do you have bedding picked out yet?
For the bathroom there are lots of possibilities. Do you have any special pictures of them at Disney, the beach or on a holiday that you'd like to hang up because that's a great place to start? I chose to do one bath in a sort of classical/victorian style because I had these goregous pics of my DD in black and white that looked really old-fashioned that I wanted to hang up. It's not overkill, I just went with some old-fashioned fixtures, a big gold mirror, light pink walls and subtle paisly shower curtain (along with the pics). More girly than anything. For the other I had some beach pics so I went with modern fixtures, blue walls, lots of glass and put out a bowl of shells (along with the pics once again). Since it's for the kids, I think it's great to have them as your inspiration. Just pull the colors/style out of the pics and go from there.
I can help you a little more once you have your basic ideas down/can see them.
