Which of the following tools is essential for assessing a toddler's gross motor development?

The correct choice highlights the importance of manipulative toys in assessing a toddler's gross motor development. Gross motor skills involve the larger muscle groups and the ability to perform movements that require coordination and balance. Manipulative toys, such as balls, ride-on toys, or push toys, encourage toddlers to engage in physical activities that are essential for developing these skills.

Using such toys allows caregivers or educators to observe a toddler's ability to run, jump, climb, and maintain balance. As toddlers interact with manipulative toys, they practice and refine their gross motor skills in a playful and engaging manner, providing a clear insight into their developmental progress.

While visual aids, rubberized flooring, and safety gates have their own roles in a toddler's environment, they do not directly facilitate the assessment of gross motor skills in the same way that manipulative toys do.