Several, many and (a) few would be adjectives of number, where (a) little and much would be adjectives of quantity. That seems to be useful nomenclature... if it exists. Some would appear under both classifications, as would lots / a lot of and plenty of.
I prefer to think of some as the indefinite plural article, however:
The apple, the apples
An apple, some apples
You should be able to find some worksheets by googling the appropriate grammar term. I have seen a lot of them, but offhand cannot recommend any single site.
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