Given the simplicity of the movie itself – which is primarily composed of episodic run-arounds – the over-arcing plot connecting it all really needs to be a bit tighter, giving us a reason to care.
These are familiar plot beats, and they are the most simplistic manner possible to mine dramatic tension from the relationship between Peabody and Sherman. We get a plot about child services plotting to take Sherman away from his adoptive father, and Sherman’s obligatory rebellion against his father’s rather heavy-handed style of parenting.
The movie is less successful when trying to mine that relationship for dramatic tension.