The first of everything infidelity related is always very difficult. Turn the day around and make some new good memories.
Since you have younger kids, I would throw a family party. Just because it's Oct 9th, special meal, cake, leftover party favors, games, balloons,singing, EVERYTHING to celebrate. What are you celebrating ? You survived and you're gonna be OK.
Tell the kids from now on Oct 9th is a celebration of all of you being so blessed to have such a wonderful family . It's your day, cry in silence or celebrate your family's love.
You will never look at Oct 9th the same when every year, you celebrate your blessings.
Big Hugs !!!!