I think it depends on the people whether kids draw the couple together or drive them apart. Whether each individual has a team perspective (we are a family, a team, we are all in this together, and one of our primary missions is raising great kids), it can strengthen a marriage. However if you are individual-oriented kids take a sh+t ton of time, work, energy, money. If you have the view the kids are a burden or taking away from things you would rather do that person can become resentful or withdraw from the relationship. Double if one of the kids has special needs. In retrospect I think this was the precipitating cause of my marriage break up (than the later infidelity) because after we had our 2nd child, who is a handful, that's when he started drinking more, taking off, leaving me alone with the kids, etc.