Not specifically in this case, multiple siblings riding together implies a higher level of safety.   BUT anyone who thinks that women or children are safe on a street or bus is either male or privileged enough to have never been physically interfered with.  1 in four women (men too) have been sexually assaulted by adulthood.  A lot of subtle and damaging interference can happen, even on a crowded bus.  And has no one witnessed the catcalling videos?  Do you want your 8 year old to have to process "show me your pussy hot mama" just because you remember the good old days when YOU walked to school?  Also, what about the trauma of being bullied?  How much of that takes place on the bus or on the street?  Tons of it.