Visit by a group of elementary school children
In this scenario, you write about your child's reactions after a group of elementary school children visits the preschool. You may of course speak to the teachers directly instead of writing in the renrakucho.
You may choose whether or not you wish to write about your child's attitude before the visit. Since these visits are school events, you are not obliged to thank the school for them. However, if you feel that the teachers really made an effort on behalf of your child, you may of course choose to express your thanks.