Have you thought of setting up cameras to try & catch which one it is? What about putting a bell around one of the cat's necks that way, when it happens & you hear the bell tinkle you'll know which it is or maybe separating the two temporarily? Cats are funny creatures. When a change in their environment happens, like a new baby, they may change their behavior, their stress levels can elevate or they become very frustrated & just can't express themselve like we can. Sometimes change doesn't affect them at all & some breeds really change their behavior. You didn't say what breed they are or if they've been spayed/neutered. Maybe they're being territorial w/the new baby thinking the baby is some type of 'threat' to their environment or maybe they're possessive of you & feel very jealous of the new baby...having to spend more time w/the baby than the cats. If you live in a neighborhood type area then it may not be a good idea to let them out unless you have a screened in porch or closed in porch type area to let them out on, otherwise yes, they MAY run off, get runover or someone may take them so you may want to microchip them if that is your choice to let them out. It's a simple procedure & my cat didn't even seem to notice them injecting the chip in. That way, you can register your cat online in their database (the microchip company) in case they do run off or someone picks them up, they can be scanned & hopefully returned to you. Another worry is that they may get runover if left outside. I think indoor-outdoor cats are more happy b/c they're not indoors all the time & can get fresh air, etc. but if they're not used to being outdoors, they may not know what to do as far as their 'boundaries' lay (i.e. not running off). That's a hard situation to deal with. Some cats just cannot behave in a new situation & yes, you may hafta give the cats away b/c of this. There ARE other cats that behave VERY well w/children or have been around children/babies so if you have to find some new cats then I'd look on the SPCA type shelter websites like petfinder.com or even the Siamese cat rescue which is a WONDERFUL rescue (they have other cats besides Siamese if you don't want a Siamese), places like that will generally post online what the cat is used to being around like kids, babies, dogs, etc or if it's a single cat only household required. There are a great many cats who WILL behave themselves & unfortunately if you don't know which one of yours it is that's peeing then you may HAVE to give them away. Good luck & hope these suggestions help!