Questions are never a problem, Im just sorry that everyone was busy and that you didnt get an answer more quickly.
What are your night time temperatures?
Usually brooder temps start at 85 to 95 degrees and are dropped 5 degrees per week, but I start about 85 and drop the temp a little more quickly for waterfowl. Just make sure that your heat lamp does not heat the whole brooder. In fact, in your warm weather, you probably dont need an actual heat lamp, more like a regular light bulb in a clamp or desk lamp that can be over one end of their brooder. Not over the water.... It should only heat one end so that they can get away from the light if they get too warm. Be especially careful during the day to make sure they arent overheating.
Marbles or rocks are usually put in the waterer for chicks and can also be used for goslings but only if you make sure that there is still enough room for them to get their bigger beak into the waterer. They are less likely to fall in and drown because they are bigger, but then I guess it depends on how big your waterer is. Certainly it would be fine for the first few days or a week, but after that it really shouldnt be necessary. You will more likely be trying to stop them from swimming in their waterer by then, LOL. If you put the waterer up on top of something to raise it to their chest height, they will still be able to reach it and will not be able to get in it.
Waterfowl are very hardy and in the wild would be swimming right away. The problem with having them swim when you are their "mom" is that they .... and you..... dont know how to preen them to get them dried and fluffed and waterproofed. Without feathers and preening, they get soaked to the skin and can chill, plus may drown if not watched. So, if you take them for a swim, just dont let them stay in the water for more than a short swim until they are bigger, starting to feather on their belly, and preening themselves. That said, within days they can have short swims in your sink or a pan of water and then you can dry them with a towel. Currently, I have some ducklings being raised by a goose, and they started swimming in their water pans the first chance they got, but werent allowed full access to the kiddie pool until they were big enough to climb in by themselves, at about 3 weeks old. I just always checked to be sure that they could get out, too.
You can take them out during the day right away, in your warm weather, but they are too young and small to be outside unattended unless they are in a cage of some sort. And then, make sure that they have shade. Waterfowl tend to overheat quickly.
I think that they are quite capable, with supervision, to be outside and swimming and sunning themselves, eating grass, and running around at a fairly early age. But again, if they dont have a mom to protect them..... then you have to be sure that nothing gets a chance to eat them.
If it has water in it....... week one.
Waterfowl grow really fast...... Week three.
Walking tall ....... week five
swimmer..... week five
chel