I did this for a challenge a while ago, when I was writing the Joy Marriot series. I know Joy isn't in it (as requested by the poster), but I still like it.
Disclaimer: Criminal Minds and all recognizable characters are not mine. Alex is.
Hush Little Baby
Derek stood over the crib, watching his son. Alex was sleeping on his stomach, knees tucked under him, one thumb in his mouth.
It had been a long morning.
He reached down and gently rubbed Alex's back when the boy's eyes scrunched up. "Daddy's here, shush, Daddy's here."
He still couldn't believe the miracle he had been given. Alex was a bundle of energy when he was awake, chasing after Clooney, crashing into the couch and tripping over his toys. Then he would toddle over to Derek and lift his arms, lower lip pouting. "Daddy, up."
Derek was happy to respond, picking up his son, cuddling him close and kissing the boo-boos away.
He spun the mobile again to restart the lullaby and reached into the crib and lifted Alex up, holding him against his chest. He hummed as he moved to the rocking chair, sitting down with Alex curled against.
He kissed Alex's baby curls, smelling his unique scent and baby powder, loving the feeling of the small, warm body tucked against his. Alex wiggled closer, still asleep.
Derek rocked them, his eyes drifting close in the darkened nursery as soft strains of "Hush Little Baby" played from the mobile.