I thought that I had made the original post when I read it! My child cannot remember and follow multi-part instructions to save his life. It is a hit or miss scenario and a parent needs to closely monitor every single thing. He is also 6 years old.
In my child's school, this has become an epidemic - the principal wrote a letter to parents that beginning this month, we were NOT supposed to help students remember to take backpacks, lunchboxes, homework, notes, library books etc. He wants them to face the consequences of not remembering and hopes this will teach them to be more responsible and not forgetful. He says, the school would provide a free apple to kids who forget their lunches (they will remember to bring it the next day onwards, hopefully). And the homework will be graded as incomplete if missing and the child cannot borrow library books for forgeting to bring in theirs.
I watch my kid closely and give him hints instead of telling him what he forgot. I am hoping that spending time puzzling over what it is will make him remember it next time. I also make him repeat the instructions verbatim and ask him "what does that mean?" for good measure. I think, for him, this is related to age, stresses at school and too much stimuli in his life and little downtime. I don't see any cure for it - just more habit training.