If you are under the age of sixteen, you will not bear criminal responsibility for the crime of theft. However, if you are not criminally responsible because you are under the age of 16, your parents or guardians will be ordered to discipline you; if necessary, you may also be detained and educated by the government (Article 17 of the Criminal Law)
If you are under the age of 16, After reaching the age of 18, then: 1. Minors shall be given a lighter or reduced punishment (same as Article 17); 2. Those who attempt a crime may be given a lighter or reduced punishment as a completed offender. (Article 23)
To sum up, your friend is unlikely to be subject to criminal punishment, usually a warning or a fine followed by release. Please rest assured