Let's look at a "top ten" list, then.
http://www.scoop.co.nz/stories/WO0602/S00247.htmDai Qing, daughter:
http://en.wikipedia.org/wiki/Dai_QingJosé Bové, no children known:
http://en.wikipedia.org/wiki/Jose_BoveAmory Lovins, same as Jose:
http://en.wikipedia.org/wiki/Amory_LovinsWangari Maathai, three children (darn, guess that negates Jose and Amory not procreating):
http://en.wikipedia.org/wiki/Wangari_MaathaiDavid Bellamy, 5 children (oh fuck):
http://en.wikipedia.org/wiki/David_BellamyCan't find a wikipedia entry on Sinafasi Makelo Adrien, so dunno if he has kids. Searches for Marina Silva suggest no children.
Paul Watson, one child:
http://en.wikipedia.org/wiki/Paul_WatsonOral Ataniyazova, none that I can find, same for Medha Patkar. That's not too bad, only 4 out of 10 have children. 40% isn't so bad, except it results in 90% children for every environmentalist.
Let's look for a top 100 list, the first 50:
http://www.guardian.co.uk/environment/2006/nov/28/climatechange.climatechangeenvironmentRachel Carson, no children.
EF Schumacher, no children.
Jonathan Porritt, two daughters:
http://en.wikipedia.org/wiki/Jonathon_Porritt(I'm beginning to sense a pattern here.)
David Attenborough, two children:
http://en.wikipedia.org/wiki/David_AttenboroughJames Lovelock, no children.
Wangari Maathai, as we saw from the other list, 3 children:
http://en.wikipedia.org/wiki/Wangari_MaathaiCharles Windsor, two children, obviously:
http://en.wikipedia.org/wiki/Charles,_Prince_of_Wales(Why Charles Windsor gets 7th on this list is beyond me, but I would be happy to look at a different list.)
William Morris, two daughters:
http://en.wikipedia.org/wiki/William_MorrisAl Gore, four children:
http://en.wikipedia.org/wiki/Al_GoreGro Harlem Brundtland, four children:
http://en.wikipedia.org/wiki/Gro_Harlem_BrundtlandRichard Sandbrook, can't find any.
Amory Lovins, none known.
Vandana Shiva, none.
Ansel Adams, two children:
http://en.wikipedia.org/wiki/Ansel_AdamsFritjof Capra, none known.
Aldo Leopold, five children:
http://en.wikipedia.org/wiki/Aldo_LeopoldChico Mendes, three children:
http://en.wikipedia.org/wiki/Chico_MendesDavid Bellamy, as we saw from the other list, 5 children.
Joseph Bazalgette (another weird one on this list), 10 children (I won't count him in the end since this was the norm for that time period):
http://en.wikipedia.org/wiki/Joseph_BazalgetteJohn James Audubon, four children (won't include him either due to time period):
http://en.wikipedia.org/wiki/John_James_AudubonPeter Scott, two children:
http://en.wikipedia.org/wiki/Peter_ScottTim Smit, three children:
http://recreatingeden.com/index.php?pid=8&season=04&episode=47(Not a big fan of Tim Smit, his Eden Project is nothing more than a green capitalist invention that achieves nothing of substance.)
George Monbiot, one child:
http://en.wikipedia.org/wiki/George_MonbiotMichael Meacher, none that I can see.
Ken Livingstone, at least five children (dirty old man):
http://en.wikipedia.org/wiki/Ken_Livingstone#Early_and_private_lifeTony Juniper, three children (ironic article):
http://www.dailymail.co.uk/tvshowbiz/article-510612/Friends-Earth-director-Tony-Juniper-sensationally-quits--attacks-hypocritical-green-celebrities.htmlJohn Muir, two children (not a modern environmentalist, though; though an inspiration for us all)
http://en.wikipedia.org/wiki/John_MuirKirkpatrick Macmillan, none known (another weird entry on this list; luckily most of these people at least have a decent claim to environmentalism).
Arnold Schwarzenegger, four children (he doesn't *really* belong on this list either):
http://en.wikipedia.org/wiki/Arnold_Schwarzenegger#Environmental_recordJohn Ruskin, none known.
David Brower, four children (ironically he advocated government licensing for child bearing, mandatory contraceptives, etc):
http://www.wilderness.net/index.cfm?fuse=feature0607James Hansen, unknown.
Thomas Malthus, three children (not modern):
http://en.wikipedia.org/wiki/Thomas_Robert_MalthusPercival Potts, unknown.
David Suzuki, five children:
http://en.wikipedia.org/wiki/David_Suzuki(It seems the more well known you are the more children you must have!)
Max Nicholson, three children:
http://en.wikipedia.org/wiki/Edward_Max_NicholsonMayer Hillman, two children:
http://www.livablestreets.info/node/36Octavia Hill, none.
Dai Qing, daughter:
http://en.wikipedia.org/wiki/Dai_QingPaul Johnson, two children (another weird one on this list):
http://en.wikipedia.org/wiki/Paul_Johnson_(writer)
Paul de Jongh, unknown.
Dionisio Ribeiro Filho, unknown.
Andrew Lees, none.
Petra Kelly, none.
John Dower, unknown.
St Francis of Assisi, none.
Jane Goodall, one child:
http://en.wikipedia.org/wiki/Jane_GoodallHenry David Thoreau, none.
Sunita Narain, unknown.
Now, 26 out of 50 had kids. But of them, they produced 70 (not including 12 from "non-moderns"). Pretty telling, isn't it? Now, I am making no statement about whether or not these people are environmental activists, nor am I saying to be a "real environmental activist" you shouldn't have kids. It's just that my experience seems to be reflected by the reality collected here in top ten environmentalist lists. It seems to me that the better off you are, the closer to middle class you are, the less likely you are going to actually champion environmentalist ideals, and will instead use it as a hobby or other indulgence. But I could just be overwhelmed by cynicism after spending a lot of time around these types of people.
Also, I was probably exaggerating a bit, because there are a few environmentalist activists I have known over the years who don't have kids. I just don't know them very well anymore, and certainly not personally.