Hyphenation of compound modifiers that have written-out numeric ranges in them

There's no "perfect" answer here, because although some people might like to attach a trailing hyphen to the first "noun used within adjectival phrase" (three-, here), the fact of the matter is we don't normally include hyphens in three-year-old children OR fifteen-year-old children today, let alone for three-to-five-year-old children (or more "creatively", three- to five-year-old children).

If you do include that first hyphen (to alert the reader that you're "suspending" the semantic scope of three- until it can be "paralleled" by fifteen-), you end up being steered towards having to include the hyphens in fifteen-year-old children - which doesn't look good.

But if you refer to an indeterminate number (say, between 10 and 15) of children who are all one year old, I wouldn't complain if you wrote it as Our creche can look after ten to fifteen one-year-old children. While I don't think those hyphens are necessary, they just might help the reader recognise that in speech the hyphenated sequence would normally be spoken more rapidly, to identify it as a "self-contained unit" (multiple words representing a single noun). If you're forced to use several numbers in close proximity like this, but with different syntactic roles, any help you can give the reader / audience is likely to be useful.

According to the Hyphenation table in The Chicago Manual of Style, the rule summarizes that age terms (numeric range) are hyphenated in both noun and adjective forms. {Example: A fifty-five-year-old woman}

Note: Adjective forms (of a number) are hyphenated before a noun {Example: fifteen-year-old children}. And kept open when it comes after an adjective {Example: three- to fifteen-year-old children}.

According to the APA Publication manual, When two or more compound modifiers have a common base, this base is sometimes omitted in all except the last modifier, but the hyphens are retained. Example: Long- and short-term memory. 2-, 3-, and 10-min trials

Hope I have answered your question.