As far as on the internet goes, here's some of what I recall from websites past and present.
Usenet
There was a social group on Usenet, well before the days of the typical modern site forum and whatnot. The Usenet group was one of the first *BDL networks/newsgroups on the internet. From what I remember hearing, they had a mailing list and organised meetups and the like.
Yior
At some stage you may see someone refer to a site called "Yior". Basically, it a pedo site [rather poorly] disguised as a *BDL site. It basically hosted pictures of young children (I'm talking all ages under 10), some in diapers, some in just clothes, some not even in either of those things, but still scantily covered. Eventually it got reported, taken down and the site owner busted up by the feds, IIRC.
DPF
Taken from the website:
DPF is the world's oldest and the largest organization (by far) in the world devoted to adult babies and diaper lovers. How old is DPF, you may ask? Well, long before the Web, long before Windows, before Mac's, before DOS, almost before the first commercial personal computers were available, there was DPF. Beginning almost 20 years ago, thousands of adult babies and diaper lovers around the globe have been corresponding, meeting, having parties, finding mommies or daddies, falling in love and forming permanent life-long relationships - thanks to DPF. Since 1980, well over 15,000 people from all over the world have found happiness in DPF. It is our fondest hope that we can share this with you, too.
*CHOKE*
In regards to the *BDL scene, DPF is definitely one of the sites that has been around for a long time. It peaked for a while having been a really active place for both teens and adults alike. This continued on until people realised that it harboured quite a few paedophiles, notably the Teen Chatroom, which felt more like a pickup service for the creepy, sicko types. Surprisingly, over the years, the place has not changed design in the slightest, it still
attracts annoys people with the background, site layout and, of course, freaks many out with your typical "omg do u mess?!?!" feel to the forums. A dangerous site that, unfortunately, many new people to the fetish find before more respectable places.
Deeker
Deeker's site has been around since May of 1996 and the owner has enjoyed it's status as being one of the most popular sites for *BDL stories (read, NOT literature). I'm sure the majority of people within the fetish community would either know about Deeker's, regularly visit Deeker's or submit content to Deeker's. In its 12 years of operation, the site has maintained a steady stream of submissions.
In a more opinionated light, the site basically caters to the fantasies of the owner, having strictly dedicated the content to focus around young boys in diapers. Go ahead, try submitting a story or sighting about a girl, it'll get knocked back quicker than a skydiver without a parachute. He seems to have birthed the site out of his own ideal of a "perfect diaper boy" and ultimately centres the whole site around the notions that "all boys belong in thick, white diapers" and that they "should be highlighted and exposed at every conceivable opportunity by the females that look after them and treat them like babies".
The biggest catch to the site, however, is that he claims it doesn't support nor condones paedophiles in any respect, yet the majority of content on his site is wanking/fantasy material. A sizable portion of it involving sex between minors, forced humiliation, diaper usage and regression of minors and some other things that are child abuse by any strech of the imagination.
Diaper-Boys
Still one of the major *BDL sites in existence. Quite a large site with a huge member-base (where I assume most are more interested in the Gallery than making genuine friendships). It's not a bad site, it's just not one you go to when you are looking for something more than discussion about diapers or baby-stuff. It's usually one of the first sites new people to the fetish come across.
Although, I will mention it has had a few problems with paedophiles in the past (as if the big stamp of "Paedophiles are not welcome here!" on the front page was any giveaway). There was a case not too long ago that lead to a few tightened restrictions on the place. But all I can say is - if you are young, just take caution if you go there.
TeenBabyNet
It's a good site, I don't have too much of a problem with it. When I was active on there, there were some cool people who just made the place really special. It was the first non-creepy *BDL community I ever came across, so it does mean a lot to me. The site alone put into perspective that I could participate in this fetish and not feel awkward or disgusted about it.
As you probably can gather, I have an account on there (quite an old one, mind you - registered in April 2004, which is years earlier than a lot of the people currently using the site), but I don't really use it anymore because I made a decision to leave the site. Why? Well, for the most part it's just not as active as I liked it to be. I would force myself to not log on for a couple of days just to bring the new post count up to something substantial to flick through. That was a bit of a drag.
Other than that, for the longest time I never saw any of the admins active on the site, which lead me to feel they no longer cared about it. There was a time before my official departure from the site where I left for about a year (the same time I left TBDL.org) and I came back to all new faces. My problem wasn't so much as having to integrate into these people's way of things, it was that I felt they made no genuine effort to include anyone outside their social circle. That was fine by me, I just collected my things and left. Looking at the site now, very little has changed. The same faces are still there, it's still not very active (which is both a good and bad thing).