The most common and most likely answer to this crossword clue is the 10 letter word BEDDY-BYES
I've seen this crossword clue in The Times
B
E
D
D
Y
-
B
Y
E
S
Buddy explains!

The straight part
We know that "child’s cot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case child’s cot = beddy-byes.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 BEDDY-BYES mean?
BEDDY-BYES noun- (baby-talk) Bedtime for a toddler, going to sleep, going to bed.