Does your pre-school have any pets?
If yes:
What do you have?
How do the children help you to care for them?
What are the benefits?
What are the downsides?
Do the children ever get to take them home? ie during holidays or weekends?
If no:
Have you considered the benefits?
What would your ideal choice be?
Obviously allergies, cleaning and costs have to be taken into account, I still remember the pets corner in my childhood nursery, it was my favourite place.
We had a rabbit, a guinea pig and a few goldfish.
If you can't have live pets in your pre-school, consider toy versions. A hutch can easily be constructed out of a sturdy cardboard box, add some shredded paper and one or 2 toy rabbits or guinea pigs. The children can still help with the 'feeding' and 'cleaning out', but at least there'd be no smelly mess!