Every expanded noun phrase is a noun phrase but not all noun phrases are expanded noun phrases.
Most teachers lead with the explanation that a noun phrase is a determiner + a noun. In order to make an expanded noun phrase, children are usually taught that you add an adjective to a noun and a determiner. This would make an expanded noun phrase, but this is not the only way to make an expanded noun phrase and as such it is not really correct to teach this as the only way. It’s also quite stilted. First off, there are other ways to make expanded noun phrases.
I’ll use the noun ‘bowl’ as my example (as in the type you eat from).
any determiner + any adjective + bowl = expanded noun phrase e.g. a big bowl
It’s worth noting here that you can of course add more than one adjective (please don’t call these ‘two a sentences’, it’s a noun phrase expanded by two adjectives).
That sentence includes two expanded noun phrases and the functioning verb ‘passed’.
Now I’m not suggesting we teach children about noun adjuncts or about deverbals and all the rest, but I’d also argue that there is little value in teaching them the vocabulary of ‘expanded noun phrases’ – most people can write perfectly well never knowing that term.
Instead, wouldn’t it be nice to just show great examples by reading fantastic texts with children or by encouraging them to read as much as possible. That way, they’ll see expanded noun phrases, noun adjuncts and deverbals being used with purpose and they can see how useful they’d be as a tool in their own writing.