It's supposed to be good for young children to work with activities that build concentration, attention to detail, and fine motor skills.
So just think how much D1 must have learned while stuffing an entire mini-can of playdough through the filling hole of a water gun.
"I put my playdough inside! It rattles! It doesn't come out."
And just think how much DOB must have learned taking it all out again with a toothpick.