An excursion notice (遠足, ensoku, or 校外学習, kōgai gakushū) is the
trip the Ministry of Education's school guidebook describes as leaving
the school for an activity or a visit. The guidebook says the name, the
content and the time of year differ by region and by school. It places
the example in the first term, April to July, and says that is only an
example of a three-term year.
The paper from your school is what to follow: the date, what happens if
it rains, and the list of things to bring. A longer trip with an overnight
stay, usually in the oldest grade, is a school trip (修学旅行, shūgaku
ryokō), which the same guidebook treats as a different event.
Reply by the date on the paper if it asks for one. Verify the day's plan
with the class teacher if the Japanese is unclear.
Your child's dates, not the general ones
Add your child and ward. The timeline does the rest.