Making a baby site
I thought that storks brought baby sites, and that th sites would grow to become adult sites, then they go off to work at either an e-commerce site or get a departmental job at a portal. The toughest phase are the adolescent sites
Anyway, kidding aside, I agree with smashingred that independant documents with custom template variables for all the growth aspects (hight, weight, etc..) and use Ditto to display this as a table or grid.
the site structure would be somethng like this, using the dates of the measurement as the pagetitle.
-Growth Chart
--jan-01-08
--jan-07-08
--jan-14-08
--etc...
As for the birth date and other variables, you can set up as many Template variable as needed to personalize your data.
http://www.modxcms.com/template-variables.html