Let's talk about printing...

If you print at 150dpi, no one would be able to tell your digital pics of your daughters are digital, unless they inspect it closely. And if someone holds a pic of your daughters up to his/her nose to check whether it's digital, his/her nose ought to be punched. (I'm guilty of doing that... Lucky I haven't been punched yet.)

If you print at 300dpi, it would probably be impossible to tell with the naked eye that it's digital. And if someone does that to your pics of your daughters, s/he ought to be kicked where it counts.

If you print a 4x6 at 150dpi, the total # of "dots" is (4x150)x(6x150) = about 1/2 million. So, theoretically, 0.5MP should be enough... You go up to 300dpi, and it's about 2.2MP.
If you print a 8x10 at 150dpi, it's about 1.8MP. 8x10 at 300dpi: 7.2MP... But 8x10 is intended to viewed from at least arm's length...

Of course, MP does not translate *exactly* to dpi, and I've neglected to account for aspect ratios, cropping, etc., but y'all get the idea.

- Yaron