Having started a family recently, there is a strong instinct to move towards more secure foundations. While you may have had a lot of flexibility to scrimp expenses without children, you can't just up and move to cheaper acommodations in a less desirable school district/neighborhood/or longer commute.

Owning a home presents a long-term hedge against financial instability. Due to zoning and other factors, it's often not possible to live in areas which are "good" for children without owning a home. My particular neighborhood in a major city has low cost/quality rentals for college aged folks, reasonable subsidized housing options, and condos. If one were to rent without subsidy for a family, they would likely be pushed into a luxury unit and pay an unreasonable and highly inflationary sum.