In no particular order:
Hydrocephaly - "water on the brain": a condition where high pressure in the cerebrospinal fluid causes the fluid-filled spaces in the brain to enlarge.
Hand - over - hand: teaching an activity or skill to a child by placing your hands on the child's hands and moving them together with yours. Over time this is reduced till the child does it alone (called "fading the prompt")
GOS/GOSH - Great Ormond Street Hospital: The biggest UK hospital for children's medicine, in London. AKA "God's Own" by the medical profession.
CDC - Children's Development Centre: a group of paediatricians operating either out of a hospital or a separate unit, often the people who make initial diagnosis.
Big Mac - a very large round button, about the size of a ... er... Big Mac, which can be operated by someone with poor motor skills. Often has an integral voice recorder.
Direct Payments - money awarded by Social Services for an individual or a carer to employ directly the sort of help they would normally get from Social Services.
Portage - Charity providing one-to-one play therapy for pre-school children in the child's own home. Named after the town in the US where this service was first sucessful.
CHASE - Children's Hospice service based in the South-East
TAC - Team Around The Child: Social Services provide a liason officer for children with complex/medical needs; arranges cross-service meetings with the parents so the child's needs can be addressed holistically rather than as a list of conditions and services.