Se on helppo nakki. / It’s a piece of cake.
While in English something is “a piece of cake”, in Finnish it’s “an easy sausage” (“nakki” is that kind of small hot dog or a frankfurter sausage, to be exact).
In English, you say “to make hay”, when you use an opportunity to get the most benefit. In Finnish, you say “helppoa kuin heinänteko” / “Easy as making hay.”
“Like taking candy from a baby”, isn’t a common idiom in Finnish, but a direct translation would be “helppoa kuin karkin varastaminen lapselta”.