If any one pushed a boy (12year) and fall down...

We would like to inform you that In the event of a person beating another person, according to the UAE Penal Law, the penalty is imprisonment. The judge evaluates the period of detention through his discretion after reviewing all documents and evidence such as witness statements and medical report. If there is a medical report and if there is no medical report the judge is satisfied with the testimony of the witnesses.
Here is the text of the UAE Penal Law, concerning your inquiry:
Article 339
Shall be sentenced to detention and to fine, whoever assaults by any means the body safety of others and the assault resulted in his illness or disability to attend to his personal business for a period exceeding twenty days.
The penalty shall be detention for a term not exceeding one year and to a fine not in excess of ten thousand Dirham, if the assault did not reach the degree of seriousness mentioned in the above paragraph

You may get an innocence or a fine, and this depends on the discretion of the judge
Who can increase or decrease the penalty according to his discretion

The mother can waive the case, and if the mother refuses to reconcile in that case, you must provide any evidence in order to obtain the innocence.