ESA and child benefit

I made a claim as my son’s appointee for ESA on 3/9/18 and he has received one payment of £127 on 21/9. I have just sent back further evidence they needed regarding his education and training and have more forms to complete for a medical assessment which are due back on 10/10. They have received his sick note from his doctor and I have been advised that at present he will receive around £74 per week. I assumed it would be in his account on Friday 28th but nothing has been paid in. I now understand that I need to contact the child benefit office to inform them of this claim but I have yet to do so as I did not fully understand that I had to take responsibility for doing so. Could this be the reason why he did not receive payment and could his claim now be cancelled altogether? I am rather worried that my lack of understanding may stop him receiving ESA altogether. Is there anyone who can advise me on this, please? Many thanks.