Yes, "two-year-olds" is hyphenated when used as a compound adjective preceding a noun, such as in "two-year-olds play together." The hyphens help clarify that "two" and "year" modify "olds" collectively. However, when referring to the age alone, you would simply say "two years old."
Hyphenated
two year olds can sleep in both
not two year olds they have to be like 7
The plural form of two-year-old is two-year-olds.
yes
Two-year-olds have accidents.
It should be hyphenated.
No, "year long" is not hyphenated when used as an adverbial phrase, such as "The project will last year long." However, when used as a compound adjective before a noun, it should be hyphenated, as in "a year-long project."
To do what?
Pre construction - two words not hyphenated.
You seem to be having trouble figuring out which word is the noun that needs to be the plural. Which thing do you have more of - twenty, year, or old? Twenty years is the modifier for old. You have two twenty year olds.
in-house - two words, hyphenated.