The phrase means that twins are more difficult to raise than a child who is an only child.
Full definition
Since twins are typically a lower birth
weight than single babies, there's enough room for them to both fit in the Deluxe, which also facilitates sibling bonding and interaction.
Some people say that twins are «full term» at 36, 37, or 38 weeks, but twins do not magically reach full - term
sooner than single babies (there is some evidence that their lungs may mature sooner than singletons, but this, if true, is just one piece of the puzzle).