Background: In children with unilateral cerebral palsy (uCP), bimanual assessments mostly focus on qualitative assessments of the impaired upper limb during bimanual tasks, which do not capture the spatiotemporal coordination between both hands. Hence, we aimed to advance our understandings in spatiotemporal coordination in children with uCP compared to typically developing children (TDC) using a bimanual, asymmetrical, goal-directed task. Participants and methodology: In this observational study, thirty-seven children with uCP (11y8m±2y10m, 20 males, 16 right-sided uCP, Manual Ability Classification System level I = 23, II = 11, III = 3) and 37 age and sex-matched TDC opened a box with one hand and pressed a button inside using the opposite hand. Spatiotemporal bimanual (movement time, temporal coupling, movement overlap, goal synchronisation) and unimanual (movement time, path length and smoothness) parameters were extracted. Between groups comparisons were investigated using a two-way mixed ANCOVA with age as covariate (α < 0.05). Additionally, correlation coefficients between unimanual and bimanual parameters were calculated. Results: Compared to TDC, children with uCP were slower (p = 0.01, ηp2 = 0.13) and presented unimanual spatiotemporal deficits in both upper limbs (p < 0.03, ηp2>0.10), which worsened in children with lower manual abilities (p < 0.04, ηp2>0.19). However, they did not differ in bimanual coupling (p > 0.31, ηp2<0.03). Furthermore, slower movement time was related with increased unimanual spatiotemporal deficits bilaterally (r = 0.34–0.80, p = 0.001–0.04), suggesting that reduced performance at both upper limbs contributes to bimanual difficulties in children with uCP. Conclusions: The bilateral reduced spatiotemporal performance, related to longer bimanual movement time, stresses the importance to assess and treat both upper limbs in children with uCP.