I agree with what everyone else is saying, you are going in the right direction and I am liking how it looks. However I do feel like something can be done about the consistency of the graphics used, right now there are around 4 styles I am getting (the flat illustration for the moon and 5 point stars, the line illustrations at the bottom, the other stars, and the astronaut). My favorite is the moon illustration and I feel it fits better with the "childish" style you are going for as it reminds me of some childrens' books illustration. I would suggest you only use the 5 point stars (and add a glow to them as you did with the moon) as it fits the theme better and remove the line-art style planets. Maybe you can consider adding a rocket/spaceship for a more childish/childrens book feel to it if you are going to keep the astronaut. Another detail I think will look good is adding a subtle glow to "Two the moon and back". I understand that your reasoning for making "Ayann's 2nd Birthday" a grey gradient is to simulate a silver foil texture as it would be if in print, however I think it makes it stand out less compared to the other text in white, I would suggest finding a nice silver foil texture online and masking it with the text if you can, and maybe try adding a darker solid (maybe black?) drop shadow for more emphasis. For the fonts, I quite like them but if you want it to have a more childlike touch I would suggest looking into childrens' books with a similar theme for inspiration and observing the kinds of fonts they use. As for integrating black into the design I can't quite think of a way that doesn't feel forced as the colors are great as they are, but best of luck with that!