Yeah, as I said, it's scary but it's rare.
Well I'll give you all the facts. This is from memory so please excuse me if I get some of the figures wrong.
I think it can produce toxin between 10 degrees and 50 degrees C. When rice is dry it's just dormant so it's no issue but as soon as you start to get it wet, there's a risk. The biggest risk though is that it's not killed by the cooking process and other bacteria are. I think you need to cook it at 121 degrees for 10 mins or so from memory(!) and bear in mind even if your oven is at 200oC, the rice will be below 100 because it's in a liquid.
So, once you've cooked it, as it cools, the longer it spends between around 50-10oC, the bigger risk there is. So if you are going to reheat it or serve it cold (and I don't because I'm risk averse), cool it as quickly as you can. With normal long grain rice, I'd do this by running it under a cold water tap but with pudding rice if you've made it in a pan, I'd spread it out thinly on a tray and chill as soon as cool enough to do so putting it in a tub once cold. With baked rice pudding it's much harder and the centre of it would stay hot for quite a long time so I wouldn't recommend it.
Make sure your fridge is below around 5oC ideally.
Then if you did chose to reheat, you need to do it quickly to again minimise the time it spends in that temperature zone. The worst thing to do would be to take a big dish of baked rice pudding and put it in a cold oven which slowly comes up to temperature and slowly reheats.
So in summary, if you are going to eat cold or reheat, do it very quickly but the best thing to do is to make and eat fresh as that's the lowest risk thing to do.
I didn't want to scare you with the death thing, it would be very rare to die of this (I had b. cereus food poisoning in India before I learned about food safety. It made me feel horrible and weak but I was ok.) You've probably had it if you've ever had a dodgy Chinese or Indian takeaway then been sick an hour or two later. That all said, with small people I'd rather not take the risk!