Child commits offense while 16. He is
only adjudicated (no disposition) before
he turns 17. Child turns 17 and starts acting
up in his CPS placement. Can we now file a Motion for Disposition even though
he's turned 17?

My reading of Section 51.0412 says yes. But
I wanted to double-check.

You're correct, no "issues" until he's 18.

I believe that *18* is the important age for your problem. See In re N.J.A., 997 S.W.2d 554, 555
(Tex. 1999)("Because an adjudication must necessarily precede a disposition, and the juvenile court does not have the authority to conduct a disposition hearing of a juvenile once she is eighteen years old, it follows that the juvenile court does not have the authority to adjudicate a juvenile who is eighteen years old or older either. Logically, once a juvenile becomes eighteen, the juvenile court's jurisdiction does not include the authority to adjudicate the juvenile.")