I don't understand! My people aren't making babies anymore! They made 1 I think and now no one ends up having a baby. So basically I have nothing but adults and teenagers running around so I can't get the shells and butterflies.....what am I doing wrong??

Where are you in your game? Is it the beginning? Witch level of medicine do you have?
At the beginning, you must insist a lot! Don't forget that women older than 50 years old can't make babies

18-50 years old can breed

but in almost 240 minutes
you can do it

For Woman, it's 18-50
For Man, it's 18+

Women who are 18-49 can produce babies (women 50 or older cannot). Also, if there is not enough housing, they will breed but not produce babies.

Thanks everyone. I figured out that persistance pays off!!