The following information is from BART:

Children soliciting funds or involved in any expressive activity under a BART permit must be accompanied by adults at all times and are only allowed to solicit donations after school hours and for limited hours on weekends. Other changes include the ratio of supervising adult to every minor and the proximity the adults must be to the children they are supervising.

Revised Language

BART’s new expressive permit language is as follows:

• Minors.  Within these Rules, “minor” is defined as an individual under 18 years of age, other than a legally emancipated minor.  Adult supervision is required at all times if an expressive activity involves the participation of minors.
• Adult supervision shall be maintained at a ratio of one (1) adult to every three (3) minors (for example, if there are one to three minors, at least one supervising adult is required; for four to six minors, at least two supervising adults are required).  The adult supervising the minors must be physically present and within five-ten feet of the minors at all times.
• Inadequate adult supervision of participating minors is a ground for revoking a permit and denying future permits. Solicitation by or Involving Minors.  In addition to the requirements expressed in Rule 6, minors are only permitted to solicit or be involved in solicitation between the hours of 4pm-7pm on weekdays and 9am-7pm on weekends.

For more information, please visit BART.gov.

Article source: http://blog.sfgate.com/incontracosta/2012/08/12/bay-area-rapid-transit-bart-revises-permit-rules-relating-to-minors/