The most common and most likely answer to this crossword clue is the 7 letter word TODDLER
I've seen this crossword clue in The Guardian
T
O
D
D
L
E
R
More clues leading to the result TODDLER
- After time more unusual accepted learner’s young child
- Young child left in care of stranger after court’s conclusion
- Duke told off Queen’s small child
- Colourful spot set up to house large and small child
- Barber and clerk stripped youngster
- Kid‘s tearful at first, left in care of stranger
- Short drink relative knocked back, just a little one
- Child beginning to trust stranger crossing line
- Toper’s opening more rum taking large tot
- Feeble walker is old, retd, drunk
Buddy explains!

The straight part
We know that "youngster" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case youngster = toddler.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 TODDLER mean?
TODDLER noun- A young child who has started walking but not fully mastered it, typically between one and three years old.