Under Texas law, expungement
is available only if the charges are dismissed or you are found not guilty.
Even if you committed the offense, however, and are convicted or plead guilty, you can ask for "deferred adjudication". This procedure essentially allows you to defer the finding of guilt until after you have finished a period of probation. If you complete probation successfully, the court will dismiss the case, which would allow you to then request expungement.
Finally, if you are convicted or plead guilty and cannot obtain a deferred adjudication, there is still one alternative available to prevent the conviction from being made known to potential employers. This is a Petition for Non-Disclosure, which you would file with the court. If the petition is granted, court officials and law enforcement will be prohibited from revealing the conviction to third parties, such as potential employers.
A park curfew violation seems to be the kind of offense which would be appropriate for either a deferred adjudication, followed by expungement, or an order of non-disclosure.
Good luck with the case and finding employment.