If they develop a tuber, they're not moonflowers. It sounds like they could possibly be four o'clocks. These Do from tubers. Moonflowers are vines with white flowers that bloom at night. Four o'clocks are somewhat bushy and bloom in the afternoon. Without scientific names, there's no way to be sure. Plant them in sun and see what you have.

Moon flower or Moon vine? Common names for these plants are among the most deceptive and confusing.
If it is pink moonvine, Ipomoea macrorhiza, it will develop a tuber. It is not as floriferous as I. alba and the blooms are not as large, but they are nice to grow. The seeds for I. macrorhiza are large, smooth and dark colored.
If it happens to be a Datura which is sometimes called Moon Flower, the seeds will likely be beige and somewhat flattened. Brugmansia (also sometimes called moon flower) seeds will be rough and corky.

Poisondartfrog, yep, they're the Ipomoea macrorhiza. Based upon their description, I think I'll stick to the old fashioned moonvine (Ipomoea alba).

Brad AKA Moonwolf

Nothing like an incomplete or wrong answer to get people to respond. I'm glad pdfrog responded. I learned something new too! :)

Oh, and pdf, thank you so much for the extra variegated money plant seeds in our trade. They have germinated and I have set them in the ground.