A kid cannot attend Kindergarten when they are not potty trained unless they have a health issue or they are autistic etc.
If the child is special needs or is autistic or the child is incontinent then they can attend kindergarten wearing diapers or pull ups.
However if the child is normal and has no health issues then the child must be potty trained before they will be enrolled into Kindergarten.
But like I mentioned if your kid is in need of diapers for incontinence, autism or other disabilities then they will be accepted into Kindergarten.
Also in most places a child who is attending Preschool must also be at least partially potty trained although they can wear pull ups.