My kids making a mess of their rooms is a daily occurance.
It's normal for things to move slowly at the distributor.
It's not unusual for him to make mistakes.
この場合、次のような言い方ができます。
ーMy kids making a mess of their rooms is a daily occurrence.
「うちの子供達が部屋を散らかすのは日常茶飯事です」
a daily occurrence で「日常茶飯事」
ーIt's normal for things to move slowly at the distributor.
「代理店の動きが遅いのは日常茶飯事」
この場合は、It's normal ... を使って言うと自然な感じで良いと思います。
ーIt's not unusual for him to make mistakes.
「彼がミスをするのは日常茶飯事」
こちらも It's not unusual ... のように言うのが自然だと思います。
ご参考まで！
That the children make a mess of their rooms is an everyday affair.
That the agency's work pace is slow is an everyday occurrence.
It's pretty much an everyday event for him to make a mistake.
ご質問ありがとうございます。
① "That the children make a mess of their rooms is an everyday affair."＝「子供たちが部屋を散らかすのは日常茶飯事だよ。」
② "That the agency's work pace is slow is an everyday occurrence."＝「代理店の働くスピードが遅いのは毎日の出来事だよ。」
③ "It's pretty much an everyday event for him to make a mistake."＝「彼がミスをするのはほぼ毎日の出来事だよ。」
ご参考までに。
カナダ 
アメリカ合衆国 
