When crossing a road, some groups will use this call as each rider crosses. People tend to rely too much on the rider ahead and just repeat the call without really looking . It is better to train each scout to look both ways before crossing. If you do decide to use it, I suggest you have an older scout or adult ride ahead of the group, cross the road and stop where he or she has a clear view of both directions. Later you may want to go to each scout calling out as he crosses.
Helmets are a controversial topic in some groups.
You either hate them or you love them. The BSA supports the use of helmets and requires their use by all riders on all BSA sanctioned rides. In addition, many states require them for all youth riders. Consult your states bike laws for age requirements. Considering that you will usually have a number of scouts who are inexperienced in group riding, following BSA requirements make sense.