Today I took the day off because of my child's seven-five-three festival.
ご質問ありがとうございます。
「今日は子供の七五三で会社を休みます」は英語で「Today I took the day off because of my child's seven-five-three festival.」と言えます。
seven-five-three festivalに関して、説明したいなら、長い和文も英訳しましょう。
下記の英文の通りになります。
Today I took the day off because of my daughter's seven-five-three festival. This festival is celebrated in Japan for the children who are turning 7, 5, or 3 years old to wish for their health and growth. We go to a shrine and later go to a photo studio to take family photos.
My eldest daughter is 3 years old and my other child is 1 year and 11 months so I would like to celebrate for both of them together. It's usual for the children to wear a kimono for this event but I'm a bit worried because they are just small children and who knows how it'll go at the shrine visit and photo shoot.
ご参考になれば幸いです。
Today is my child’s shichigosan so I will be taking the day off.
「今日は子供の七五三で会社を休みます」
- Today is y child’s shichigosan so I will be taking the day off.
七五三は英語に訳せませんのでそのままで良いと思います。
Taking the day off = 今日休みます//一日休みます
「今日は子供の七五三のために会社を休みます。
Today is my child’s shichigosan so I will be taking the day off.
七五三は７歳と５歳と３歳になった子供の健やかな成長を祝う日本の文化で、神社にお参りに行き、そのあと写真館で家族写真を撮ります。
It is a Japanese tradition to celebrate the healthy growth of children aged 7, 5, and 3 by going to a shrine and taking a family photo at a studio afterwards.
上の子が３歳で、下の子はまだ１歳11か月なのですが、一緒に３歳のお祝いをしてしまいます。
My oldest child is 3 years old and the younger one is only a year and 11 months but they will celebrate too.
着物を着せるのですが、子供たちがまだ小さいので、着付けやお参り、写真撮影までうまくできるか心配です」
We will make them put on a kimono but the kids are still small so I’m worried if we will be able to safely dress them, pay respects at the shrine, and take pictures.
アメリカ合衆国 
