I hope my wife doesn't read your post - I'm 40, and have been telling her for several years now that it is too late, and I am too old, to become a dad. Anyway: It's not clear to me if you're asking the question "what is the best technology I can use to capture the most information about this object" or "what is the best/safest means I can use to store these images, once recorded, so that they have the best chance of surviving many years". On the first question, it absolutely doesn't matter. By the time this creature is old enough to be looking at these images, the technology you used to capture them will be long obsolete regardless of what you use. People our age grew up with scratchy, poorly-exposed 35mm color prints and Super 8 film of ourselves. Our parents grew up with some black and white photos, some color. The thing you have to keep in mind is that unless you happen to be a president, serial killer or rock star, these recordings are of absolutely no documentary interest whatsoever to the world at large and have no intrinsic value. The only purpose they serve is to remind you, and the kid, and potentially a few family members or friends, of the occasion that is being recorded. The quality of the recording is immaterial because it's just a stimulus to unlock a memory cascade in you, the viewer, who was present at the event anyway. And those memories will be much higher quality than any recording you can make. You could create a daguerrotype, use a brownie box camera, or aim a hand-cranked silent movie camera with B&W film and the pleasure you get from watching the result at a later date will be absolutely identical to that you'd receive from a 3D IMAX recording with octophonic sound and Feelarama(tm). TL;DR: don't sweat the tech, because it won't matter. 10 years from now you'll look at whatever you recorded and think "that ancient tech was so quaint", regardless.
The second question is more interesting. There is no storage medium of high enough density for your needs that will last "indefinitely", and you also have the fun problem that codecs evolve. You should absolutely not use any file format that doesn't have an open-source decoder (not that there are many of those in common use these days). And as for the physical storage of the bits, you'll have to keep rolling them from media to media. Since most people can't be bothered making offsite backups, etc - I'd advise picking two disparate technologies for your backup strategy, e.g. writable DVDs and hard drives, and refresh them regularly. If you're comfortable with it, paid cloud storage is also an option (again, diversity is your friend - one copy on amazon and one copy on google and you can be fairly sure a single disaster won't wipe out both).
Frankly, you probably don't feel this way right now, but if you think back objectively to your own childhood, you'll know that 99% of these irreplaceable memories sit in shoeboxes from the moment shortly after they were developed to the moment they're rummaged through while people are sorting your estate. So, don't over-invest in this.