No Teachers are not legally allowed to wipe children's bottoms or get anywhere close to their private areas because they could be accused of molestation or touching a child in the wrong place which could get them into trouble with the law.
A school nurse however could help a child cleanup if they have an accident such as if they pooped their pants or peed their pants then the school nurse could assist the child in getting cleaned up.
However a 5 year old or 6 year old child should be able to properly wipe their own bottom and change their clothes and underwear.
If the child is in pull ups they should be able to put a new pull up on as well.
If a child is going to school they should be wiping their own bottoms as well as changing their own clothes.
I remember being in Kindergarten and I had pooped my pants due to diarrhea and my parents brought me a change of clothes.
I cleaned up myself and used a shower we had in the school to take the shower and then changed my own clothes.