This is a very common concern with moms who are overwhelmed looking after one child and can't imagine looking after 5 kids let alone them all being young and needy. To ease her mind say things well remember I am not getting up in the night for feedings, or doing the bath and bed routine - yes we all know we still work all evening but it helps to say this. Remind them that parents of twins and triplets abound and manage just fine - it is all about getting a routine and rhythm and then go on to say how much experience you have in daycare - ie lots of time to practice. Talk about the ages being close so they will all grow up together and how it is easier to have them all doing the same things instead of waiting their turn while you deal with the older kids and not having school age means no bus runs so no disrupted naps or wasted travel time.... make it sound like it is a positive thing.