Some baby shower card sentiments that work for both baby boys and girls are, "Enjoy every minute! They go by too fast" and, "Congratulations! We're excited for you both and hope that your new baby is happy and healthy. All the best!"
For a more formal baby shower at which the guest is not very close to the expectant parents, possible sentiments include, "Congratulations on your upcoming new arrival!" or, "Wishing you all the best with your expected bundle of joy!"
A more casual, warmer sentiment is, "Congrats, we are so happy for you! Enjoy your journey into parenthood and have fun! We wish all the best for you three in the coming months." If it's a girl, some possible sentiments include, "So excited to hear about the new little lady in your life!" or, "Your little princess is here! And she's just as beautiful as her mommy!"
If it's a boy, some sentiments are, "I heard there's a handsome new man in your life! I can't wait to meet him!" or, "Congratulations! We can't wait to welcome your new little man!" To write something with a little humor try, "Let the noise begin!" or, "Kids cry, throw fits, eat all your food, and keep you up all night. Don't worry, that's only for the first 18 years!"