I LIKE beads... there's a reason why rosaries are usually made of beads (as well as buddhist prayer beads)... they're comforting to roll between your fingers, don't catch on clothes, and are good for those who have a thing about counting. In this case, if each bead represented a child, going bead by bead would make sure every child was prayed for.
I would VERY much recommend round smooth beads, with little silver or golden spacers between each. Ideally with the first letter of each child who is going on mission written on them. ((One can buy special ceramic or metal or stone paint pens at art stores so any ceramic (or glass... technically the ceramic pen is one that adheres to glass, since that's what glazing is) or metal, or stone bead can have the child's letter calligraphic onto it.))
If I were making them I would look for mikimoto pearl sized beads, and ideally, use a paint that's a light color against a darker background... to avoid the alphabet bead look. <grin> But then again, alphabet beads would work in a pinch.
OR I'd snag sandalwood beads and use the little burning tool to calligraphy each child's initial on the beads.
LOVELY & caring idea your churchmembers are doing, btw.