They're all pretty violent. They were little mockery of goverment at the time, not really kid stuff. It's funny because now in days some people get carried away with "hidden meanings"
I remember talking about this once, someone brought up the rhyme that goes "Mary, Mary, quite contrary, How does your garden grow? Silver bells, and cockle shells and pretty maids all in a row" my friends response was "She did it!! She killed them and burried those poor girls in a row in her garden!! *foamspaz*"
Lol now I hardly think that's what it means, but my personal opinion, I'd say Rock abye baby or Three Blind Mice.
Three blind mice, three blind mice.
See how they run! See how they run!
They all ran after a farmer's wife,
Who cut off their tails with a carving knife.
Did you ever see such a thing in your life,
As three blind mice?