Meaning "small lump or mass of something soft" is from 1749. Dab hand is British slang, 1828, from dab "expert, knowing or skillful person" (1690s), said by OED to be "school slang," of unknown origin, perhaps from dab in the "strike lightly" sense.

What does dabble mean in slang?

: to take part in an activity in a way that is not serious. : to play or move around in water. See the full definition for dabble in the English Language Learners Dictionary.

What is a dabbling child?

All children dabble occasionally. It is when a child consistently dabbles that intervention is needed. Dabblers are generally unengaged. The role of the teacher is to bring the child into meaningful engagement with materials and with the child's peers.