I recently painted a fun mural for a friend's nursery. I was asked for simple scenes with friendly animals, in muted colours, that would work for a girl or a boy. 
I started with sketches of various combinations of animals and foliage, and put them into photos of the room to decide the best scale to paint them.
I did one of the sketches in colour, to show how they would all look on the pale yellow walls...
... and then put together a colour pallette. I used the same colours in all three scenes, to hold the room together. Eventually I did add one additional colour as I was painting: a pale orange for the lion.
This is a photo of the elephant scene half-way painted. It shows the building up of the layers of flat smooth colour.
And here's a photo of all three finished painted scenes, after they were given a final protective coat of varnish. I love how they came out.
Can't wait for the baby to arrive now and see if they like their room!