The only difference is the size of the pasta. Tortelloni are slightly larger (5 grams) than the Tortellini (2 grams). Tortellini comes in Three Cheese and Cheese and Spinach flavors. It was made smaller so that it would be versatile in making meals for young children as well as adults.
Tortelloni are stuffed pasta, the same shape as tortellini, but larger. Although either can be filled with a wide variety of foods, meat-based filling as less common in tortelloni. Tortellini may be served with sauce or in a broth; tortelloni are rarely served in a broth.