First of all, I used the same font and background color.
Then I traced the cartoon face and hair from reference by using a pen tool. I used different layer for each different part such as hair and face.
After several traces, coloring and gradient, one cartoon character is finished and ready to change position.
I placed him in proper position based on my sketch.
For star, I used a star tool to create stars. Then I arranged it in proper position based on my sketch.
To play save, I've convert all font into outlines because not all computers have the same font.
For the inside of the birthday card, I've copy the cartoon character and transform it by reflect it in vertical.
Then I slightly rotate his head and delete his right arm.
After that, I copy the right and transform it by reflect it in vertical axis.
I've changed the background color and again, used the pen tool to create a speak bubble.
Adding the text inside the speak bubble.
Then change the stroke of the speak bubble to make it much more beautiful.
Finally, It's finished.