There is nothing wrong for adults or those who passed the age of maturity to watch cartoons if these cartoon films do not contain anything objectionable or harmful from the Shari`ah point of view. For example, a Muslim is not allowed to watch cartoon films that display porn stuff. So, the criterion is the content of the cartoon films. If it is acceptable from the Shari`ah point of view, then it is allowed for the young and the old, the child and the adult to watch it. It is important, however, to note that, like any other permissible thing, watching cartoons should not distract the person from fulfilling his religious duties such as prayers, being dutiful to parents and so on.