I don't offer baby's first year packages to my clients, but there's one little thing that I say during a newborn photography session that almost guarantees they'll come back for 6 month and 1 year photoshoots.
When I have the baby posed in one of my newborn posing beds, I say "when you bring her back for her six month and one year sessions, we'll put her back on the same bed so we can see how much she's grown. And you'll have a nice little set of three matching pictures for your wall."
This is an EASY way to get them back again without having to offer them a discount.
Better yet, let them know that if they schedule their 6 month session and 1 year sessions within a week of the newborn session, they'll get a free gift. You can give them a collage that shows a picture from each session or even an individual print of their favorite portrait from each session. I give my clients who come in more than once during baby's first year a free 11x14 from each session. It only costs me $5 but it has a high perceived value, and it works!
Go ahead and try it. Come back and leave a comment to let me know how it goes!