If your child is under the age of 13, then you will need to stay with them for the duration of the Dojo. For children over the age of 13, it is recommended that a parent/guardian remains nearby and can be easily reached by phone. This is in the interests of safeguarding.
Many Dojos will have a designated table for parents/guardians to sit during the session, where they can work, read a book or have a chat! Alternatively, parents may like to get involved in the session by helping out e.g. by setting up the equipment or preparing snacks. Some parents get involved by becoming mentors themselves.