What does it mean to be in Mission? To be missional?
A mission committee that I served with was actually asked that question for something as mundane as updating a website. What does it mean to be missional? And from there you can go into many different theological conversations, but for fun you might not want to do that with children. Not just yet.
For me, as a Christian, I am being missional when God compels me to act on the behalf of someone else. Whether or not it benefits me, and although rarely planned that way, I am often the beneficiary. It is not simply a matter of serving others, lots of good people serve others, it is a matter of doing whatever it is at the bequest of God. And, not to put to fine a point on it, when I offer to others this gift from God and tell them that it was God that sent me, I wander into my definition of evangelism. It is a fine line, but one that I am comfortable in stepping over.
Ministry is what the church does for those that show up within the physical structure of the building. It is directed by God, supplied by those who love God, and offered to those that show up. Mission is what the church does for those outside of the physical structure of the building. It is directed by God, supplied by those who love God, and offered to anyone. Mission becomes evangelism when we tell others who sent us. Ministry fills you up, so you can be emptied out in mission.
And, if done well, it all becomes a thin place.