Seeking Moms of 2Boys.

I went with colors more so than a specific theme...I was able to find cute sheet sets in coordinating but not matching decor and they love it...you have a pretty good age gap there so I wouldnt pick anything too permanent but maybe allow the older brother to choose...since really little brother doesn't even care at this point!

I have two boys! They are closer in age though. I love to look at ohdeedoh or cookie mag for decorating advice on children's rooms. They have some good ideas at making a room not too "theme" oriented that kids grow out of quickly, which is good for a baby and an older child to share.

Maybe decide on a color your older son likes, and use that as a base, like yellow and grey or something. Then just accessorize around that neutral palate, with themed things the children will like, but will be easy to change out as they age.

http://www.ohdeedoh.com/ohdeedoh/home-tours

A cushy floormat or rug would be great. Maybe one w/ a road, houses and trees on it so the older one could drive cars on it, and it will give the younger one something to look at while crawling.
And colors- lots and lots of colors!
:) Good luck! :)

http://www.ohdeedoh.com/

search joint rooms, or shared rooms. there are a ton of ideas. love that decorating kids site.

We did a camoflauge theme in our boys room. Painted camo on the walls...much easier than you think.

I think a sports theme would be good. They make stuff for both infants and older kids.
Check walmart.com and target.com to see if you can find some that would mesh well.

I let my older son pick what he liked first. He into the transformers/robots, and cars. Disney makes some great thing for both babies and older kids. For my boys room, i did bright reds, blues and yellows and stuck with a car theme.

Maybe a space theme. You could have robots and planets on the 8 yr old's side, and stars and moons on the babies?? You could even hang some Styrofoam planets from the ceiling.

You might want to try a tropical/surf theme...The walls in a nice yellow, celeste colored ceiling, surfer bedding for your eight year old and surfboard or tropical (dolphins, fish, etc,) for the baby.

In one house I painted the room white, put a chunky car/truck border around the middle, at chair rail hieght. I dipped one of the bulldozers in asphalt colored paint and drove him all over the bottom half then cut out some of the trucks from the border and stuck them on the top half.
I then took the asphalt paint and some yellow and painted the window sill into a road with lines and a stop sign
We had the racecare bed and the cityscape rug. I just bought sheets with cars on them from Target. My son was between 2 and 5.

In this house I painted the room a deep tan/brown, almost the color of package tape. I painted a plaid design under a fish border. He has a latch hook rug with a guy fishing hung on the wall with a fishing pole and post cards of freshwater fish framed with rustic frames from Michael's. I buy his sheets from Target and Walmart. He is now 9 and we have been here for 4 years.

In another house we put granite paint on the bottom half, a wolf border in the middle and grey on top. But this was for my then 14 year old.

Solid primary colors are a great choice--think anything in the "basic eight." We even took a thin piece of plywood, had it cut into one 4x4 sheet and four 2x2 sheets and painted them in reds, greens, yellows,blues, oranges, and black for huge wall hangings--nice when you live in a white-walled rental!

I have 2 boys who are COMPLETELY different from each other in likes and dislikes. The only thing they have in common are they are extremely proud to be American. We painted the bottom half of their walls dark blue and the top half bright red with the white ceiling. We got a border that has American fighter jets and the American Eagle and American flag across it. The boys absolutely LOVE their new room. We took a picture of the Thunderbird jets while they were in the area and blew it up to poster size and hung that. My older son (9) said every morning he wakes up he smiles as soon as he sees his room. It looks really good. They originally wanted me to paint the American flag along the wall that has no windows but I told them that was too time consuming.

My girls are sharing a room and I got lots of ideas from Pottery Barn and Land of Nod. Since we are on a budget.... I got my ideas from those stores/magazines and purchased similar looking stuff at Target, Walmart, and Ikea. If you want the bedding to match You can purchase the matching quilts/comforters at Pottery Barn and then suppliment the rest of the linens, furniture, etc. buy using a neutral solid color like white, cream, or blue that you can find at Target in both the crib sheets and twin/full sheets. I had to have a queen size bed and a crib in the room so it was tricky finding stuff. Now my youngest is two and they both share the queen size bed. It would have been better if I could have had a twin bed and a crib and then moved up to two twin beds. Something else to consider... my sister in law did two twin beds on a platform twin frame. This made the beds closer to the floor so it was easier for the kids to get in and out of. This eliminated the purchase of a toddler bed for her. Also, if you don't have a lot of room.. you need a tall vertical dresser instead of a horizontal dresser.. this allowed room in our girls room to also have a play table. Ikea has a great tall dresser (i think it comes in white and blue) and a great choice of table and chair sets for kids. They also have containers and cube storage options at Ikea and Target that seem to work well for sorting toys. I put baby toys on the bottom and 8yr old toys up higher to keep little parts away from the little one.
Good luck and happy shopping.