Making watercolor objects in MidJourney is quite easy. However, sometimes you do have to fight with MidJourney to get what you want. Let’s experiment with different styles.
Prompt: a chicken, watercolor, white background, detailed

Right off the bat, you can see that this is indeed a rooster not a chicken but I’m going to roll with it.

Also, you can see that adding the word ‘detailed’ it gives a very detailed water-colored painting. It’s quite impressive. Adding the words white background will put a white background. Otherwise MidJourney will give you a farm or some other background.

Let’s try this again and remove the word detailed and replace it with simple.
Prompt: a chicken, watercolor, white background, simple

This looks good but I want to to be even simpler. Let’s add in ink and watercolor. This gives MidJourney two different ideas as to what to draw

Prompt: a chicken, ink and watercolor, white background,
This looks good but it needs something more. Let’s add farm core art style. Why? I don’t really know, it just sounds good.
Prompt: a chicken, ink and watercolor, white background, farm core art style

This looks a lot better. Let’s make some variations and render out an image.
Variations

Upscale

As you can see this is done very well. It was hard to get it simpler. I really wanted something drawn much simpler. Either way, I think it looks good.