Grandad you are just experiencing guilt that your lovely g.son was injured due (in your mind) to you. It does happen and in all probability your g.son has totally forgotten the whole incident now. You will goon feel ing guilty for much longer.
When my children were young (and I was a foster parent also), I used to say that being a Mother meant going tobed every night feeling guilty. Most days I had done and said something that I regretted, or NOT done something I wished I had.
With wtrhen taking one of my g.children (aged 8yrs) to an after-school music class, I tripped and fell over quite badly. Knew I done some real damage to myself, took a while before I allowed any of the many peolle who rushed to my aid to get me up, and eventually paramedics took us both to hospital. Although everyone was good at trying to reassure g.daughter, she was very tearful and as the ambulance turned into thehospital grounds and she could see her Mum witing for us out of the rear window - I heard her heartfelt explanation of 'Mummy' and felt so very guilty.
She acted it all out by taking the temporary sling I had been given by the paramedics and putting it on her own arm the following morning as she went into school. Made me feel worse when I heard of this.
However, when I talked to her (now 20 year old) about this incident a few days ago, she had only the very vaguest memory of it. Mine is still very clear and sharp.
Passports not in the drawer I always keep them in. Turning the place upside down.