I am not sure if you are writing about the past or the present. However, only the second sentence has a correct verb form (for the present continuous). There is no verb tense which has the form "are play". "were played" is the past simple passive form and so does not make sense here. I don't know how you learn English verbs but one idea to have in mind is that every verb tense has a fixed form (or structure) for affirmative statements, negative statements, and questions. If you have a list of these available, it could help you to check when you have created a new form by mistake. If you don't understand this point, don't worry.

Can a Chinese speaker who reads this question please help this student? Thank you.

If you are talking about the present, the only option there is the second one.

Start with Today is Monday. The children are playing on the playground.