Arielle McKidd filed legal docs, obtained by TMZ, seeking to end the couple's 5-year marriage ... citing irreconcilable differences. She's asking for joint physical and legal custody of their two young children, Aiden and Nava, and wants to hash out splitting up assets and the like in mediation.

One other thing ... Arielle is also asking the court to restore her original surname, Goldrath.

She says they got hitched in 2017, but the date of separation is listed as "TBD." Kevin announced they were splitting up earlier this summer, around early July.

At the time, he wrote ... "I don’t often share my personal life on social media, but today there is something I do want to share with you. A few months ago, Arielle and I decided to end the marriage portion of our relationship. We reached this conclusion after much soul searching and discussion. We know it’s what is right for both of us."

KMD had some kind words for his estranged spouse, adding ... "Arielle is an incredible mother to Aiden and Nava. She’s one of the wisest, most intelligent and loving people I’ve ever known. We continue to have the highest love and respect for each other."