The most common and most likely answer to this crossword clue is the 7 letter word TRIPLET
I've seen this crossword clue in The Daily Telegraph
T
R
I
P
L
E
T
More clues leading to the result TRIPLET
- A little journey presumably for one of three children
- Blunder allowed in one of three
- Expedition allowed to make notes
- Little error allowed in what musician might play
- Person with siblings allowed to go on holiday
- Journey allowed one of three to share birthday
- Journey permitted making a few notes
- One of three allowed to follow tour
- One of a number of children sequentially evident in Alcott tale
- One of three allowed on outing
Buddy explains!

The straight part
We know that "One of three kids" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of three kids = triplet.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 TRIPLET mean?
TRIPLET noun- A group of three.
- One of a group of three.
- One of a group of three siblings born at the same time to the same mother.
- A group of three notes played or written where two notes would ordinarily be; a form of tuplet.
- A triquark.
- A quantum state with three allowed projections for the spin.
- A constructed gem consisting of a thin slice of natural opal sandwiched between a clear glass or quartz top and a synthetic or stone backing that enhances the colour of the opal.