>>123732052The timeline in the film from when they first meet til when they adopt the puppies probably takes place in under a year. It’s pretty reasonable that they were just enjoying their marriage for a little while before trying for kids. Heck, it could be they were trying but just hadn’t succeeded in getting knocked up yet in that small time frame.
Also, they only decide to keep all the extra puppies at the end because Roger had just gotten an enormous payout for selling his song, and they’re like, “why the hell not? We’re gonna buy a mansion anyway.” After the events of the film there’s every reason to assume they would have the room and money to have a kid on top of keeping the dogs.
When they decide to keep the fifteen puppies originally before their big payout, they actually struggle a little with the decision because they know they’ll have to stretch money and make sacrifices. But then the decision is finalized purely because Roger just wants to spite Cruella that fucking bad. At first they seemed to think that getting rid of the litter would beca matter of course, but then Cruella rolls in and pushes Roger into keeping the puppies just as a “fuck you.” It never had anything to do with how much he was or wasn’t fucking his wife, and everything to do with exerting his dominance over his wife’s friend.