Following obstetrical brachial plexus injury, infants are unable to learn specific patterns of movement due to the disruption of neural pathways. Even with successful reinnervation (spontaneously or post surgical reconstruction), function can be suboptimal due to overactivity in antagonist muscles preventing movement of reinnervated muscles. Botulinum toxin type A (BTX-A) was used to temporarily weaken antagonistic muscles early in the reinnervation process following brachial plexus injury, with the aim of facilitating functional improvement. A case series of eight children (five females, three males; mean age 12.5mo [SD 6.43]; range 5–22mo) with significant muscle imbalances but evidence of reinnervation were given BTX-A injections into the triceps, pectoralis major, and/or latissimus dorsi muscles. After a single injection, all parents reported improvement in function. Active Movement Scale total score changed significantly between pre BTX-A and 1 month (p=0.014), and 4 months (p=0.022) post BTX-A injection. It is proposed that BTX-A facilitated motor learning through improved voluntary relaxation of antagonist muscles while allowing increased activity in reinnervated muscles.