If a boy is very clingy to his mom, does the following sentence sound natural?
The boy is attached to his mom all day.
I'd appreciate your help.
The words clingy and attached are both figurative and literal; they refer to emotional dependency which may manifest itself in physical ways: the child might want to have his hand held, or might want to hold onto his mother's dress.
The phrase all day runs counter to the figurative meanings, and so one would assume you had only the literal meaning in mind, that the mother has him "in tow" all day, or that he's close by her side. It would not necessarily imply any sort of emotional dependency.