If dishonesty is the only route to go, just say you have been saving bit by bit for months for such a purchase. In reality, you could just do this now and have a kit in six months... It's not like they don't come up for sale all the time. But with a baby on the way, and if the purchase is really to save those precious moments, and if your current cameras don't cut it, go for it and make up for it later. Cut $10/week from your personal spending---most of us probably spend more than that on coffee and/or beer.
I put about $20/week aside for photography. At the rate I shoot with everything else going on in my life, about half of this goes to film or chemicals and the rest towards savings for gear or whatever. $500 or so a year isn't that much, but it does go a long way, especially once you have a kit set up already.