Deaf children not exposed to signing often invent their own form of sign language, which they use (or try to use) with their families. What’s it called?

Answer:
Home signs. To communicate properly in sign language, deaf children need interaction with experienced signers. Lacking this vital exposure, they make valiant attempts to communicate on their own. Researchers, such as Susan Goldin-Meadow and Adam Kendon, have studied and documented some of these invented signing systems, which are occasionally quite elaborate, but none of them are known to have achieved the complexity and cohesion of a full-fledged language like ASL.