Can cerebral palsy, global developmental delay and mental retardation coexist in a 6 y.o.?

Yes: All neurological problems are tips of the same iceberg, most types of brain problems have multiple manifestations, some are just more obvious than others.

2/3: Global developmental delay is a term used for younger children, replaced by intellectual disability, the newer term for mental retardation, at age 6 if criteria are met. 50% of childten with cerebral palsy have intellectual disability; 40% have epilepsy. Vision and hearing impairments are common, also.