My DC (11) witnessed a collision between 2 vehicles. They saw everything, helped the injured driver and came and found me who called an ambulance etc. My DC was happy to be a witness and has completed the witness statement from police.
However, there is the option to say whether you want your name and address details to be released. My instinct is to say no. I've no idea if including name and address would potentially put DC in any danger or if it would make any differene to the case anyway in the offchance it did end up going to court.