S.H.
When a child is tired or over-tired, they tantrum. They do not have the advanced communication nor emotional ability... to be articulate yet. They don't even have, fully developed emotions yet, much less the understanding of the abstractness of it nor do they even know the 'words' for their feelings...much less the ability to tell you. Hence they tantrum.
I learned, that for my kids, I did not go out and do errands with them, when it was nap time. Nor when they were tired or hungry. Bad timing. Kids when tired or hungry, have, nil... patience and they get over-stimulated easily. That means, they will melt-down, easily.
When tired, and in a store or running errands, it causes over-stimulation.
Kids also, tantrum/cry... in order to SHUT-OUT... stimulation. To stop it. That is the only way they know how to communicate that. It is a coping thing.
When my kids are tired, they can't even eat... even if they are hungry.
So I always had dinner, earlier for them. Because once they were tired... they could not eat and/or would be very fussy, at dinner time.
Kids also need.... to be verbally cued... to be told what is coming up. To be given a head's up. They need to be, "transitioned" to things. Not abruptly.... having activity changed or stopped suddenly. They need to, transition.
Always also, let a child know what is coming up and what is going to happen. So they can get used to it. ie: "In half hour, after eating, we will run errands. You will sit in the cart... then we come home and nap."
Even if they 'understand'..... it does not mean they can do it. At these ages.... a child cannot necessarily do, everything that is in their heads. At these ages... there is no coordinated ability, per what is in their head's and what they can actually do.
ie: if you show and explain to a 2 year old, how to ride a 2-wheel bike. They may understand. BUT that does not mean they can do it. Because, their motor-skills and coordination... or muscle movements, are not there yet. Not like a 7 year old, in comparison.
Keep expectations, age appropriate.
At this age, they don't even have, fully developed impulse-control yet, either. And they are reactors. They don't even have cause & effect, down pat yet... nor do they even have fully developed attention spans, either. Nor do they have understanding of socialization or social skills.
Get the book 'What To Expect The Toddler Years."