Chocolate & Thundercats - The creating would take less energy than you might think; the images I create for t-shirts, mugs etc are all digitally painted in Photoshop (yay for Adobe giving CS2 away for free! 
), and the majority of the designs I have up at the moment were painted as part of a "30 in 30" project - 30 paintings in 30 days, so one a day. They're speed paintings; each one took maybe an hour or two tops, painted in the evening after putting DD3 to bed. The shop is here. Generating more artwork for products is actually the easiest part. With Cafepress, I just have to upload the art, choose what to put it on, and Cafepress handles the rest. For actual physical stock, quite a few printers allow you to upload artwork then they print it on t-shirts, mugs etc and ship it to me; most craft fairs take place at weekends, so OH would babysit whilst I went off to run a stall - plus a couple of friends organise craft fairs and would be willing to take my stuff along to sell on their stalls. And I'm good friends with the owner of Phoenixx Rising, a mail-order alternative-wear shop, and we've been discussing me producing some exclusive t-shirt designs for her.
It would all fit in around kids pretty easily and would be perfect - there's just the not-so-minor stumbling block that having initial stock printed up for craft fairs would cost m £200-£300 that I just don't have right now.
Does Mumsnet have a section where I can advertise myself? I was wondering if there'd be interest in custom painted portraits of people's babies?
We'd planned on holding off until I' had at least one cycle, preferably 2 before TTC, so I figure that gives me a couple on months in which to try and make this start to get off the ground - at least in terms of portrait commissions & Cafepress sales, anyway. Plus painting is therapeutic and keeps my mind off other things. (Like the fact that three friends all gave birth this week, and another just announced her pregnancy. 
)