Assign each family group a putt-putt golf hole to design.  You could do this in two different ways.  You could gather the supplies and have them choose from the supplies you have supplied to build.  Or you could give them a two-week window where they can design from their own supplies at home.

On the designated night, give each family unit a time limit to build their golf hole.  This could be done outside if your church has the property or inside if your church has the space. 

After the build out is done, you walk through and assign par to each hole.  Then turn everyone loose to play it.  

Don't forget to invite the rest of your congregation to play putt-putt too.

Notes:  Since getting that many putters and golf balls may prove difficult, try using hockey sticks and tennis balls.  Or croquet mallets.  Be sure you tell the families to build for these types of balls.  

And if you have hyper-competitive dads, you may want to put a spending limit or other limit so you can avoid that one monumental golf hole.