For the past 8 years, we've been creating a Good Friday morning service for and led by children because almost all of them have the day off from school. We base the service on the workshops we've been doing during Lent (some years, for example, we memorize Psalm 23 or the Apostles Creed and use that in the service).
We have a chapel which is just the right size (seats about 75 folks). We also have a children's choir that helps provide music. And we do communion "by intinction." A big part of the Lenten preparation is usually devoted to Last Supper/Communion. For the sermon we've often done a question and answer format between the Director of Christian Education and the Pastor. Questions like: "If this is the day Jesus died, why do we call it 'Good' Friday?" The Q&A seems to work well at holding the kids' attention, but the "sermon" is less than 10 minutes.
We do the service at 10 a.m.; it's over by 10:40 and gives families a way to observe Good Friday without spending the whole day at church.
Anne
I've attached the actual "order of worship" for one Good Friday, as a example -- this must of course be adapted to your church's worship style. There's no need to copy the very "high church" style our church uses, just follow your own traditions. The Bible Background from that year shows that we had studied the Lord's Prayer. But we also "rehearsed" the "order of worship" or at least several parts of it in ever workshop.