Have you tried an aqua painter pen? It is perfect for adding that watercolor effect without all the mess. Look at this cute card set you can make with it and the Barnyard Babies stamp set from Stampin' Up.
The aqua painter pen is super easy to play with and when the water is gone, just unscrew the top and fill it up - really inexpensive! Check it out in my online store...
The Barnyard Babies stamp set can be used for other occasions too!
Here is the Sweet Lullaby designer reversible paper used on these cards:
You can purchase all of these Stampin' Up items in my online store....here are some more ideas using the aqua painter: