I'm all for the banter of getting everyone signed up, but I do think it isn't a decision to be taken lightly.
Like NurseR I have 2 kids (4 & 6 too). I travel a lot for work, so can train as much as I want when away. When I'm not away I have to cram everything in to the remaining time. I train before the kids are up, or after they're in bed, or at lunch where possible. I spend the weekends doing long rides and long runs, wishing I was at home with the family.
My wife works p/t so it has made life a little easier, however she is now topping her hours up, which means that schedulling needs to be planned at the beginning of the week.
She's used to looking after the kids when I'm away, but it is a little unfair on her to do so when I get back so I can train. I have pre-emptively retired from IM after Outlaw, until the kids are a lot older. It's not fair on them or the wife.
For those of you in similar positions please think carefully. Fink recommends a 'family meeting' where you explain what you want to do and the time it will take. I think to those that are not as involved as us, it means nothing. Telling people you'll be training 12-15 hours a week at some point means nothing until it actually happens, when life gets in the way and plates start to get thrown.
There are ways around this of course - a turbo allows you to stay in and train whilst freeing up t'other half. Same with a treadmill (though I don't have one). Swimming could be done during the kid's swimming lessons. We did a shift change at one point. I swam, she arrived with boy for his lesson, we all swam, I took the boy home. She continues her swim.
Don't go in with blinkers on thinking it will all be OK. Keep your eyes open and be flexible. Once I stopped worrying about doing the plan to the letter life got easier. Communication is key.
If it wasn't for the iron support I get at home, I couldn't do this.
Enjoy it!
Hope this helps!