observing the children in our after school club ?

i can anyone tell me should we be observing the children in our after school club and if so what format we should be using ie written visual etc i know that we need to be using the eyfs on the younger childrenwho attend but it is difficult as some children only attend some sessions once a week be great ful for your help as i have only stepped in as deputy due to people leaving and understand the importance of observing in a creche setting