R7 or R/RP for shooting my toddler?

Forget the R and RP. They're full frame cameras, and you'll need all new lenses. You could use the lenses you have, but you would be using less than half of the camera sensor, and you wouldn't be getting the best out of either lens or camera body.

There's a myth that full frame cameras will give you better low-light performance than the APS-C cameras like your camera and the R7. That's not quite true. A full frame camera with an appropriate, large-aperture lens will get you better low-light performance. At considerable additional cost. In other words, you would need at least one new lens. And besides, you can get that low-light advantage, only if will accept only a narrow depth of field, and are willing to take great pains and care to focus accurately. (Some people want a narrow depth of field, and so require a full-frame camera with a fast lens. I don't recommend that for moving children, and I suspect that you're the type of person to do that. For children, keep it simple.

The R7 will give you fabulous low-light performance. (Keep in mind that all cameras require some light to make pictures, but the R7 will do the job just fine unless you live in a cave.)  The R10 would also be good -- probably plenty good -- but the sensor performance is not quite as good as the R7 sensor.  (There's no way to know whether you would find it good enough, but I'm pretty sure I could make it work.)

For children, I suspect that you won't have much use for your 10-18 mm lens, however. An ultra-wide lens like that is good for photographing large environments, but not so good for children.

Start by taking many pictures of the family that you have now. You'll soon learn what you need and how to do it. Your current camera will actually work well for this. I recommend that you keep the camera near at hand and ready to go on a moment's notice. That's how you can get great photos of children.

My suggestion is not to try for ultimate image quality.  To do that, you would probably sacrifice some emotional content, and that's a bad tradeoff in my opinion.  Think about why you want the pictures.