handful
Something or someone that is difficult to manage. Joan's daughter is very polite and well-behaved, but her son is a real handful, always getting into trouble. This project seemed easy at first but it has become a real handful, and I'm not sure I'm going to finish by the deadline.
*a handful
Fig. someone, often a child, who is difficult to deal with. (*Typically: be ~ become ~.) Bobby can be a real handful when he needs a nap.