Preach the gospel.  Occasionally, I run into children's ministries that just play games.  They have all fun, but little to no learning.  I personally (and this is just my opinion) don't think that does a lot of good.  Don't get me wrong, play is important, and play is actually one of the better ways for kids to learn, but there are times to play, and times not to.  I do plan play periods during each service, and special events for the kids just to play and fellowship with each other.  But every service and all of the service is a little too much.  We don't want service to be boring, but we don't want service to be fruitless either.

Give the kids a time to play and fellowship, but give the kids the word of God as well.

The age of the kids should determine the amount of play time.  The younger the children, the more play time.
Also, if you attend a church that has marathon services, you might want more play time.  We want to minister to the kids, but they will only retain so much.  For a rule of thumb, if my church service runs two hours or more, I usually have a 1 1/2 Children's Church, and 1/2 hour of play time.
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