When our oldest son was four, I set out to teach him as many Bible verses as we could muster. He was a quick study (aren't they amazing?) and soon had put 35 verses to memory.
Recently I realized I hadn't worked nearly as hard with the other children on memorizing Scripture. And as I was reorganizing our memory-work box, I came across the little homemade cards we'd used with our firstborn. Really, nothing special or fancy but they worked. And so I made everyone else their own "Ten Verses" cards and we set to work. Upon completion of each verse, they get a sticker next to the reference. Even the 11-year-old still loves this.
The added benefit, of course, is that I get all of those verses written on my heart as well.