Compared with young children with unilateral CP, children with bilateral CP showed greater variation in Mini-MACS/MACS levels, and both sub-groups showed large variations in AHA or BoHA units. The classifications and assessments used in this study are useful to differentiate young children's ability levels. Such information is important to tailor upper limb interventions to the specific needs of children with CP.

Manual Ability Classification System levels and Assisting Hand Assessment/Both Hands Assessment performance at 18 months are important predictors of hand use development in cerebral palsy (CP). Children with bilateral CP improved less than those with unilateral CP. Children with bilateral CP and symmetric hand use reached higher limits than those with asymmetry.

Aim To describe the development of hand use during bimanual activities among children with unilateral cerebral palsy (CP). Method A cohort of 166 children (79 females, 87 males; age range 18mo–13y, mean [SD] age at first assessment 37.6mo [20.5mo]) with unilateral CP, registered in the Norwegian CP Follow‐up Program with two or more Assisting Hand Assessments (AHAs), were included in this longitudinal study comprising 524 AHAs. Developmental limits and rates were estimated by non‐linear mixed effects models and compared between a stable limit model (SLM) and a peak and decline model. Development was described according to Manual Ability Classification System (MACS) levels and AHA performance at 18 months of age (AHA‐18). Results Children in MACS level I, or in the high AHA‐18 group, reached highest limits and had the most rapid development (p<0.001). The developmental trajectories were different between MACS levels I, II, and III and between the high, moderate, and low AHA‐18 groups. Seventy‐five per cent of the children reached 90% of their estimated limit at 5 years 10 months or earlier. The SLM showed the best model fit (Akaike information criterion: 4008.99). Interpretation Most children approached a steady performance limit before 6 years of age. Although children in MACS levels I and II reached 90% of the expected limit at 3 and 4 years respectively, the corresponding age was 8 years for children in MACS level III. The better model fit for the SLM indicates that children with unilateral CP maintain their attained limit of hand use to at least the age of 13 years. Development of hand use between 18 months and 13 years follows a stable‐limit pattern. Most children reach a steady limit on the Assisting Hand Assessment before 6 years of age. Manual Ability Classification System levels I, II, and III represent distinct developmental trajectories, level III having a slower rise. Early hand use is an important indicator of future development.

Parents reported that the children's everyday activities were utilized as opportunities for training, hence describing the intensity of therapy merely by counting minutes or number of sessions seems insufficient.