My daughter was 9 when she started growing breast buds. I took her off of commercial milk (switched to a milk without hormones or antibiotics) and her buds dissappeared. She is 11 now and has natural (her own hormones causing them not artificial from cow's milk with additives) breast buds. When she started growing breasts this second time, I bought her a couple of training bras, one really nice and lacy in her favotire color. She already has 3 different types of deodorant, and sometimes needs it. :P She has read several books on womanhood and what to expect from many different viewpoints. I made sure that she knows that a lot of people are uncomfortable talking about it, and that in the past it was very common for a woman to think of her private area and sexuaity as dirty or disgusting, and some people sadly still do.
I have also started a wemooning box for her. She knows about the box, but not what is in it. I don't let my girls play with makeup, and when they start getting buds, they can use clear lip gloss and nail polish only. When she becomes a woman she will be allowed colored makeup, and we will go to a friend's house to get a mary-kay makeover (free) and buy her some colored makeup. We (DH & I, she has no clue) are also planning a big fancy dress-up dinner at a local seafood resturant where she will get her very own lobster tail. *smile* (she's never had lobster before, but loves seafood) We will talk about the water in the ocean being affected by the moon, and her new connection to the earth and sky. I will give her her wemooning box as well on this day, and she will likely call everyone in the family to brag. *blush*
In her wemooning box (a large, plain wooden box) right now is:
*A list of websites for budding women printed on fancy paper (including beinggirl.com which is by a pad/tampon company and advertises makeup, but is still a great site nonetheless.)
*A small box of disposable panty-liners
*A carrying case for small tampons, full of the tiniest they make (holds 3 discreetly)
*2 tubes colored roll-on glitter
*3 small colored nail polishes
*2 large disposable pads
*2 meduim disposable pads
*A wood-burning kit, ladybug stencils, paint, & brushes (for decorating the box so she can pass it down to her children)
*2 containers lightly-colored glitter lip gloss
*2 new unfolded cloth diapers (great for travel showers, cleaning house, using as a headband or emergency pad, etc)
I also plan to put in there a couple dozen hand-made cloth pads, same amount of cloth panty-liners, a home-made fancy-paper one-use, no expiration, coupon book (for things like buying condoms, washing your laundry, doing one of your chores for you, an extra hour of computer time, a backrub, I won't ask just this once, etc in it)and a new journal with a fancy pen.
My mother was very matter-of-fact about bleeding, we had no celebration, it was just "well, let's go buy you some things then". I want more for my girls.
----------------------------------------------

As for boys, There is a ceremony held by a local pagan group in my area every year at their yearly campout for all boys who aged to 13 in the past year. The men all go out together for 4 hours with the boys and talk to them about what is expected of them as a man, what they should expect, and proper behaviors, etc. When they come back, there is a huge feast, dancing, drumming and a grand bonfire. The boys are crowned with grasses by the girls who have come of age (and spent some of those 4 hours making the crowns).
I don't have any boys, but If I did, I would probably make a gift box for them as well containing things like a journal, a how-to book about sex, a coupon book, a make-your-own cologne kit containing their favorite scents and bottles, the box-decoration kit (with their favorite thing as a stencil), A list of websites for newly-matured men. and of course, 2 new diapers. :P I would probably also wait until 6 months after their 13th birthday so the day would be special.
---------------------------------------------------

Either way, when a child reaches adulthood, they gain the benifits and responsibilities of being an adult. In my home, the aquire bills (in direct proportion to their income, and which go into a special savings account/buy bonds for when they move out of the house/turn 18), gain an additional small chore or two, are allowed to leave to approved places an simply leave a note (as opposed to having to ask for permission), get a phone in their room, and get to stay up one hour later than usual.
I know, I type too much sometimes :P