In schools at least, some variation of this question is reasonably common – people worry either that a vagina isn’t big enough to accommodate a penis/sex toy/ tampon, or that it will become stretched out of shape by any of those things.
The vagina is a tube, about 8cm long. It isn’t quite hollow – but it can stretch a lot. To make space for a baby’s head, for example – which is much bigger than pretty much any penis.
The vagina might change shape after childbirth (after any number of children). But the idea of it becoming ‘baggy’ is probably more of an exaggeration.