Can a kid be capable of killing an untrained adult with krav maga if they were 4'8 or 5'1?
It all depends on the skill level of the “kid” (do you mean a child?)
If you mean an actual child, then I don’t think a child would be capable of killing an adult based on skill alone, I guess? Size and weight have to be considered, along with years of training, precision of technique, etc. A child could probably, if trained hard enough, incapacitate an adult or get away from an adult long enough to get help or something.
If this is a question based on the credibility of krav maga alone, then I think any martial art can be lethal if trained consistently enough 🤷🏼♀️