Infants who sustain an injury to the brachial plexus in the perinatal period are at high-risk for long-term neuromuscular deficits and prehensile dysfunction. If recovery is delayed because of slow axonal regrowth, disuse atrophy and secondary musculoskeletal deficits may develop. The investigators' hypothesis is that early, intensive intervention designed to foster muscle activation is essential to optimize outcomes after brachial plexus injury and may supplement rehabilitation and microsurgery. This proposal targets infants who are non-surgical candidates. Yet, future studies will examine whether the investigators' experimental intervention can hasten recovery from microsurgery and will examine which post-operative time-point is best to employ it. The investigators' intervention shows promise to increase muscle activation and improve arm function in infants with brachial plexus birth palsy (BPBP) through contingent reinforcement based on a pilot study.

The investigator's study objectives are to (1) test the feasibility of a parent-lead in-home 2-week intervention for infants with BPBP; and (2) determine the effect size for the primary outcome measure(s) in preparation for a future definitive randomized controlled trial (RCT). In this feasibility RCT, the investigators will compare two in-home interventions in 3 to 12-month-old infants with upper trunk BPBP; n=12 per group: (1) experimental; and (2) dose-equivalent active control. For the experimental intervention, infants will trigger a musical toy to move and play via biceps contraction above a preset individual threshold. For the control intervention, toys will be available to play with, yet, there will be no reinforcement for biceps activation.

Inclusion Criteria:

1. Age of 3 to 12 months with upper trunk brachial plexus birth palsy confirmed by an attending Hand and Upper Extremity Surgeon;
2. Full-term at birth;
3. A minimum score of '1' (0-7 scale) in elbow flexion of affected arm (isometric contraction) based on the Active Movement Scale (AMS);
4. Score ≥ 25th percentile on the motor subtest of the Bayley Scales of Infant and Toddler Development, 3rd Edition (BSITD-III®);
5. Ability to sustain attention/arousal for a 10 minute training period based on criteria from the Neonatal Behavioral Assessment for an awake-alert state.

Exclusion Criteria:

1. Visual/auditory deficits;
2. Nerve repair/shoulder surgery;
3. Excessive crying during session(s);
4. Shoulder, elbow, or wrist joint contractures > 20° in the affected arm;
5. An inability to trigger the musical-toy to play at baseline.

Blind to treatment group