Conductor Keith Lockhart and members of the Pops orchestra performed a few yuletide tunes for the kiddos at the Boston Children’s Hospital Tuesday. The baton twirler was joined by former Patriots receiver Troy Brown, who narrated “?’Twas the Night Before Christmas,’’ and vocalist Maureen McMullen. Afterward, Lockhart and the Pops headed to Spaulding Rehabilitation Center for a performance for patients, doctors, and therapists.