This is a great question. It is best to start with a definition of infant and toddler. Infants describe children until around the age of 1. Toddlers describe children until around the age of 3. It is important to keep the ages of children in mind to be precise on what is appropriate and inappropriate.
Let me list several things that would be appropriate:
First, safety is the most important. As such a young age children will not be able to watch over themselves. So, the adults need to create a safe environment.
Second, the ratio of teachers / caregivers to children has to be reasonable. To watch children's safety properly, you will need to have trained people and enough of them.
Third, toddlers can move around and even learn a good amount. In light of this, it would be important to intellectually stimulate them to a certain degree. Hence, there should be at least one teacher who is trained with infant and toddler development.
In light of these point, what would be inappropriate is the lack of the above, that is, anything that compromises safety and intellectual development.