Sounds like lack of pollination. Baby squash must be pollinated in order to grow into a big squash. If it doesn't get pollinated within a couple of days, the plant will abort the squash and it will rot and fall off, making room for new baby squash. There are many posts on this site about how to hand pollinate. If you hand pollinate the babies, then they'll grow big and strong for you. Basically take the center part of the male flower (no baby squash attached) and swirl it around in the center part of the female flower (the one with the baby squash attached). It helps to remove the petals of the male first. You're trying to get the yellow pollen grains from the male flower into the female flower, which is what the bees normally would do. But there is a worldwide shortage of bees.
So Squash sex=baby squash growth.
Flowers typically open in the cooler early morning hours.
Best of luck!
Susan

I manually pollinated the female flowers and just harvested my first fully grown, healthy squash! Thanks susancol!