Three instructions at once is one instruction and two you will repeat
Shoes, coat, bag. Said in one breath, on the way past, to a child facing the other way.
Multi-step instructions are held in working memory in sequence, and the sequence decays from the end. What survives is the first item, which is why the child is standing by the door in shoes with no coat, looking — from the adult's point of view — deliberately obtuse.
Chunking is a skill that arrives late
Adults hold three-step instructions easily because they chunk them into one thing called 'getting ready'. Children build those chunks over years, and a routine that has been done identically for months becomes one of them. Until then, the steps are three separate things.
A child who does the first of three has not ignored two. They completed the one they kept.
The fix is dull and reliable: one instruction, wait for it to be done, then the next. It feels slower and takes less time.