The most common and most likely answer to this crossword clue is the 7 plus 5 letter word NURSERY RHYME
I've seen this crossword clue in The Times
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More clues leading to the result NURSERY RHYME
- Rum Henry’s stirred with rye for Doctor Foster, say?
- Tender lines by Frost, say, in something read to a child?
- Verse for young people that could be cursory?
- Jack and Jill‘s bursary taken for this?
- Jackanory versery perhaps?
- Little Bo-Peep is cursory, for one?
- Doctor Foster is one medic wildly merry and happy on vacation
Buddy explains!
The straight part
We know that "Doctor Foster, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case doctor foster, say = nursery rhyme.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.