The children laughed at that joke. This sentence is transitive or intransitive?

Transitive verbs take one or more objects in a sentence, while intransitive verbs take no objects in a sentence. Put simply, a transitive verb describes an action that is happening to something or someone, which is known as the verb’s direct object. An intransitive verb, on the other hand, describes an action that does not happen to something or someone.
www.thefreedictionary.com/transitive

Your example does not meet that requirement, so it is an intransitive verb.