In Jain Dharma, a bath with your mother is not considered a sin by itself, especially if it is only for care, cleanliness, or help.

What matters most in Jainism is:

• intention
• modesty
• purity of conduct
• avoiding unnecessary attachment or improper behavior

At age 12, it is usually better to maintain privacy and dignity as much as possible. If possible, bathe separately. But if your mother is helping you for care, that is not sinful.

If you feel confused or uncomfortable, the safest Jain value is:

• keep things simple,
• stay respectful,
• and avoid anything that may disturb purity of mind and conduct.

So, no, it is not a sin just because you are bathing with your mother.