What precautions should I take before moving my family into a pre-1978 (lead-paint-era) house?
You have to actually eat, inhale, or otherwise take in lead paint for it to cause lead poisoning: it can't be absorbed through touch.  So, if you find paint flaking anywhere, you should keep your children out of the room, scrape the flaking area (while wearing a mask), and repaint.  Then clean the area thoroughly, especially if flecks fell on anything they are likely to stick in their mouths.

Be wary of lead paint on surfaces that may become scraped/worn easily, as that could lead to lead paint fleck/powder flying around.

If you still feel concerned, you can have the house tested.  Also, be aware that US public schools are required by law to offer free lead testing in kindergarten and first grade.

Thanks to Robert for suggesting this link from the EPA on lead hazards.