A toddler who reliably fetches their shoes will frequently fail to fetch their shoes and put them by the door. The second instruction is not being ignored; it was never held.
Working memory sets a hard limit
Acting on an instruction requires holding it in mind while doing something else. That temporary store is small in early childhood and grows slowly across the preschool years.
One item fits comfortably. A second competes for the same limited space, and the act of carrying out the first frequently displaces the second entirely.
The child is not choosing which part to obey. From their position, the instruction was to fetch the shoes, and that is what was completed.
Movement itself consumes capacity
Walking across a room, opening a door and reaching for an object all demand attention at this age, because none of them is yet automatic.
Every non-automatic action draws on the same resource that is holding the instruction. The longer the journey, the more likely the instruction is displaced before arrival.
This is why the same child manages a two-part request while sitting still and fails it while walking. The instruction did not change; the competing load did.
Distraction along the route is the usual failure point
Anything encountered on the way competes directly for the held instruction. A toy on the floor is not a temptation so much as an overwrite.
Parents commonly observe the child arriving at the destination and standing there with no apparent purpose. That is what the loss looks like from outside, and it is not defiance.
Reducing what is between the child and the task therefore improves compliance more than repeating the instruction does. The route matters as much as the wording.
Sequencing works better than compressing
Splitting a request into single steps delivered one at a time reliably outperforms one compound request, even though it takes longer to say.
Giving the second step on completion of the first also builds the sequence over time. The child gradually holds longer chains as capacity develops.
Visual sequences help for the same reason. A picture strip of the getting-ready steps holds the order externally, which removes the need to hold it internally.
What changes as the child gets older
Two-step instructions typically become reliable during the preschool years and three-step ones later, with wide variation between children of the same age.
Familiar sequences run ahead of novel ones. A child may manage four steps of a well-practised bedtime routine and fail two steps of an unfamiliar errand on the same evening.
Where a child consistently struggles with instructions that peers of the same age manage, or where understanding of language seems limited more broadly, a health visitor or speech and language professional is the right referral point.