This study aimed to quantify relationships between lower limb muscle strength and locomotor capacity for children and adolescents with cerebral palsy (CP) to identify key muscle groups for strength training. Fifty 6- to 16-year-olds with CP (Gross Motor Function Classification System level I or II) participated. Isometric muscle strength of hip flexor and abductor, knee flexor and extensor, and ankle dorsiflexor muscles was measured using hand-held dynamometry. Ankle plantar flexor concentric muscle strength was assessed as the maximal number of unilateral heel rises. Locomotor capacity was evaluated by the 6-min walk test (6MWT), 10-meter Shuttle Run Test (10mSRT), and Timed Up and Down Stairs Test (TUDS). With control for age, sex, and height, hip flexor and ankle plantar flexor strength explained 47.8% of the variance in the 6MWT and 32.9% of variance in the TUDS and hip abductor isometric strength explained 43.5% of the variance in the 10mSRT. Avenues for future research include randomized controlled trials that specifically target hip flexor muscles, as this has not previously been done, and determining factors other than strength that are likely related to locomotor capacity of children and adolescents with CP.