The most common and most likely answer to this crossword clue is the 6 letter word AUTISM
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Buddy explains!
The straight part
We know that "Disease of children" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case disease of children = autism.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 AUTISM mean?
AUTISM noun- A pervasive neurological disorder that is observable in early childhood and persists throughout the lifespan, characterised by atypical communication, language development, eye contact, and sensory experiences.
- (now medically obsolete) A diagnosis involving a pathological tendency to engage in self-centered fantasy thinking, historically considered a symptom of insanity and/or schizophrenia.
- (4chan) Abnormal and unhealthy focus or persistence, and unhealthy hatred of opposition or criticism.
- The range of conditions classified as pervasive developmental disorders, generally held to include autistic disorder, Asperger syndrome, and pervasive developmental disorder - not otherwise specified (PDD-NOS). Also includes childhood disintegrative disorder and Rett syndrome.