I have two boys, one 22, one 10.
My first guy did the Mickey Mouse Yellow on the walls, then we had the sheets and comforter, posters that I framed and a small MM face rug.
He also had a wolf theme. My MIL make his curtains from material with different wolf prints on it. She also made his comforter. We got a wolf border and painted the room grey on the top 2/3 and deep gray on the bottom. He had many wolf prints and a light form MN that we hung and set in his room
My little guy had the truck theme, but I did it this way. THe room was white, I found a chunky car/truck border, this was placed about 36 inches up the wall. Below I drove one of his tractors through black paint and then on the wall. Above I hung a stop sign and put some of the chunky cars I had cut out of the border. Then on his window ledge I painted it black, actually Behr has a color called Asphalt, and painted a broken yellow line in the middle and a white line at the end for his cars.
In the next house we painted his room deep tan and had a fish border. Not a baby boy fishing border but one that you would hang in a lodge, a man's fish border. (according to my son) We then had tab top denim curtains, Target, that I hung with sticks. I had a rug hook of a guy fishing that has tab tops and I hung that on the wall with a broken fishing pole. I found postcards in MN and framed them for his wall. Under the border I painted a plaid pattern with green, yellow, blue and orange. His comforter is one we found in upper MIchigan with an Up North theme. Target had a whole line of fishing/camping themed items. We have camouflage sheets and sheets with bears on them.
This house we are painting the same deep tan. About 1/3 the way up I will paint a blue stream. Then there will be trees and animals. Some hills. ONe wall will be Spring, one Summer, one Fall, and one Winter. I found a coat hanger shaped like a moose from IKEA. Most of his old stuff will fit right in. I have used the Wallies, little wallpaper cutouts, for some details in other houses.
We have moved every three years, military.
I did a farm scene in one of the girls' rooms and a pastoral, white picket fence, trees, meadow, in another of theirs.
I have one of the One Stroke Painting books from Micheal's and it really is just that easy.