The aim of this study was to use family-assessed instruments and details of children's impairments to explore factors affecting the activities and participation of children with cerebral palsy (CP). A postal survey was conducted with families of a geographically defined population of children with CP aged 6 to 12 years. Family-assessed indices of children's activities and participation were the Activities Scale for Kids (ASK) and Lifestyle Assessment Questionnaire (LAQ-CP). Families also assessed children's abilities using the Gross Motor Function and Manual Ability Classification Systems (GMFCS; MACS). Details of children's impairments were available from the 4Child epidemiological database and used with the GMFCS and MACS as explanatory variables in multiple regression analyses to identify their effect on children's activities and participation. Families of 175/314 (56%) children returned an assessment using the GMFCS and 129 (41%) children participated fully by returning all the questionnaires. Full participants (72 males, 57 females) did not differ from those who did not take part by their age, sex, CP characteristics, or associated impairments: GMFCS Level I-25, Level II-43, Level III-15, Level IV-14, Level V-23; MACS Level I-14, Level II-30, Level III-18, Level IV-13, Level V-13. Scores for the ASK and LAQ-CP Physical Independence and Mobility domains were predicted well by children's movement, manual, and intellectual disability, and also, to some extent, by the presence of seizures or speech problems. LAQ-CP domains for Economic and Clinical Burden and Social Integration were not well explained by children's abilities and impairments. Family assessment, therefore, offers a useful method for measuring children's activities and participation; however, currently available instruments do not fully represent all the domains in the International Classification of Functioning, Disability and Health. Children's abilities only partially explain their activities and participation.