The marbles start about the size of a pea and expand to the size of a marble as the water is absorbed. When we first discovered them you could purchase them in packets by individual color or in a multipack. We started with the multipack but ended up going back for individual colors and I think Coline may have brought some home with her as a gift for her Mom and Grandma, I can't remember now. The girls bought them because of their beauty yet their creator designed them with a greater purpose. Similar to God, He didn't just create you and I to "look" a certain way. God's gifted us each differently to share our beauty with others, just like the marbles.
Think of it like this, whatever we absorb and take in, is what others will see, hear, and witness about us through our behaviors. We were designed with more care than a marble, so shouldn't we pay more attention to what we're allowing in.
There is so much available to us in the world, we need to be cautious when we absorb all that is out there. If we desire to be beautiful like the water marbles so we can share God's love with others, then we need to keep our hearts (the marble) moisturized with God's Word, the Living Water. In doing so, we fill ourselves with joy and peace. A joy and peace that will overflow into the lives of those meet.
"May the God of hope fill you with all joy and peace
as you trust in him, so that you may overflow
with hope by the power of the Holy Spirit"