We often get the question, "What is the difference between the round and the square ball pit?" Aside from the obvious different shape, the square ball pit is larger than the round ball pit. Depending on the space you have allocated to use it, either is a good option but the square ball pit will hold more balls. We recommend the round ball pit for use with up to 2-3 babies or toddlers, whereas the square ball pit can fit up to 4-5 babies or toddlers. We suggest 200-300 balls to fill the square ball pool vs. 150-200 balls to fill the round pool. As you can see from the photo, the round ball pit will fit inside the square ball pit.