Under 'normal' circumstances I don't think there would be any requirement to have anybody CRB cleared. However, it is probably a good idea to have some guidelines in place for the dealing with junior players. For example,
1. You should try to avoid situations where you are alone with junior players
Hence when you are travelling to matches think about how you can arrange pick ups/drop offs to avoid the situation where a junior player is dropped off first/last
2. Parents of junior players should provide a contact number and any relevant medical information and whether it is OK to give the player common medications (paracetamol/strepsils)
This really isn't meant to be onerous and please don't stop having junior players in the team. Half an hour of getting some good practice guidelines in place will suffice. Have a review after 3 months, just to check that there isn't something you've forgotten.