at play
1. Actively playing or involved in other leisure activities. The kids love the game you bought them—they've been at play for hours now. What do you like to do when you're at play?
2. Active or existing as something to be considered. It's a complicated matter with several important issues at play.
at play
[at this moment] involved in playing. (See also at work.) The children are at play, and I am doing household chores. Whether I am at work or at play, I try to be pleasant to people.