noun
one or two; a few; a small number
Used to indicate a small, indefinite number, typically one or two, but can extend to a few. Often implies a modest or approximate quantity.
一つ二つ質問してもいいですか。
May I ask one or two questions?
冷蔵庫に卵が一つ二つしか残っていない。
There are only one or two eggs left in the fridge.
少し is a general adverb meaning 'a little' or 'a few', while 一つ二つ specifically counts items and emphasizes a small number, often one or two.
いくつか means 'several' or 'some' and is more indefinite than 一つ二つ, which explicitly suggests a very small number.
Compound of 一つ (one) and 二つ (two), literally 'one, two', used idiomatically to mean a small number.