Basically, there are two basic rules for converting sentences from Active Voice in to Passive Voice, which are common for all tenses :
1. The places of subject and object will be interchanged in the sentence.
2. Only 3rd form of the verb or Past Participle (e.g. written) will be used as a main verb in Passive Voice.
So the passive voice for the given sentence would be:
Hide and seek is being played by him.
Note: Object(Hide and seek) which was at the last of sentence came in the beginning and subject is now at the last. Also, verb "is" turned to its past participle form "is being played".
For more understanding, please check the examples of similar sentences which are as given in the image below: