What do you think of a 2 of 3 multisig wallet both are paying into? The third key is held by someone both trust and agree on. If the husband runs away the moneys goes to the wife. If it turns out that the kids father is not the husband the money goes to the husband. You could also hand the third key to a "notar" and make a contract to spell things out. I believe that such a set up is an additional incentive for a marriage well lived.