My wife is also expecting at the end of September, and I am doing some hard core nesting by preparing the house for a larger family.

There are a number of kits, parts and hardware available out there to do any level of handrail project from fancy and spiraling to fast and affordable.

Check out the stair parts in the finish lumber section of your local home center, usually in the same aisle as all the trim and molding.

A decent lumberyard will generally stock newels, hand rail and balusters. There are oak and pine handrails that have a slot underneath that readily accept 2x balusters and even wrought iron baluster that fit into brackets you fasten directly to your treads.

Here's an ****** store that sells much or what I'm describing:

Another quick easy and affordable solution would be to close of the open side of the stairs by running a series of thick dowels or 2x slats a few inches apart from tread to ceiling. On the wall side mount a stock hand rail being sure to attach your brackets to the framing.

One last note on stairways and babies. The best advice I ever got with our first child was to teach her how to descend stairs backwards on her hands and knees, as soon as, she began to crawl. We never had an accident because she never tried to stand facing downstairs in that top heavy unstable position.