The most common and most likely answer to this crossword clue is the 11 letter word PRESCHOOLER
I've seen this crossword clue in Independent
P
R
E
S
C
H
O
O
L
E
R
Buddy explains!
The straight part
We know that "One’s probably not above five" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one’s probably not above five = preschooler.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.
What does PRESCHOOLER mean?
PRESCHOOLER noun- A child who has not yet attended school.
- A child who is educated at preschool.