Programs such as GIMP will do their best at this (sophisticated scaling algorithms), though of course it's fundamentally an unsolvable problem as no program can "restore" detail that was never there. You could try messing with blur or soften tools if the result is still too blocky. Or turn them mono or sepia, vignette them, and implicitly claim that the lack of resolution is a feature not a bug.

Though quite frankly, all newborns look the same to me. If you borrow some photos of a completely different baby then as long as you're careful with ethnic origin and eye colour you'd probably fool everyone except yourself and the missus...

Peter