If I have a criminal record and I got a petite larceny charge 1st offence what do you think would happen?

You should retain a good criminal lawyer to handle the matter and try to avoid getting another conviction or a jail term. Young people fail to realize the consequences of their actions. They commit a crime for a few dollars worth of stuff they do not even need and if they get a criminal record they will find it very hard to gt a job for the rest of their life. Once you are known as a thief or child molester no one is going to hire you and you will have to do minimum wage jobs. You will not be able to travel internationally, get government benefits, or get into some schools. You may even be denied a loan or an apartment if you have a criminal record.

First time petty theft a person should expect to have an offer of summery probation, court fine and restitution to the victim.

Probation, fines maybe a little jail. That is what probably will happen.