There isn't one. I think you heard it wrong. You may be thinking of "feeling blue" or "being blue," which means feeling sad or depressed.
a man who is liked by everyone
I'm not familiar with that idiom, but I imagine that having a big hand means having a lot of influence or authority.
explain
Idioms are hard to understand unless you already know the meaning.
fertile land
The suffix in "bluish" is "-ish," which means "having the quality of" or "somewhat." In this case, adding the suffix "-ish" to "blue" changes the meaning from simply "blue" to "somewhat blue" or "having a tinge of blue."
The meaning of the idiom dead certainty is absolutely or definitely
being caught between a rock and a hard place is one Between the devil and the deep blue sea
Idioms are expressions that have a figurative meaning different from the literal meaning of the words used, while proverbs are traditional sayings that offer advice or wisdom. Idioms often have a meaning unique to a particular language or culture, while proverbs are generally known and accepted across different cultures.
It's "remember to BREATHE"
The best way to learn any language is to use it. If you can't take the kids somewhere where they can be surrounded by the language and its idioms, you can use the idioms yourself and encourage the kids to follow suit.
Promising is not an idiom -- it is a word. Idioms are phrases.