Vision Test
Explain that you are curious to know whether or not it is true that (Tuesday night girls group, Sunday morning kids church, whatever you are hosting) have better eyesight than (the pastor, teenagers, your puppet, who or whatever you can think of).
Write the memory verse out in very large font so that it is easy to see and test the kids to see if they can read it. When they can, bring out a second copy of the verse written in slightly smaller font, when they demonstrate that they can read that too, bring out your third copy in smaller font etc.
You'll want about 4 or 5 readable ones so they learn the verse by repeating it, then around 4 that range between marginally readable and tiny so they can show off as you praise their incredible eyesight and confidently predict that the next one will be impossible for them to read.