There are many kits out there for a pondless waterfall. The "loudness" of your falls will depend on many varitables.Height of falls, amount of water falling. I have seen many pondless falls..many very beautiful with wonderful sound. Good luck!

If you can possibly put a berm (ridge or bank) of earth between your yard and the road, that is really going to absorb road noise. The bigger, the better...that and a fountain could make a huge difference.

I understand if you don't want a pond with falls, I hope you can build a dissappearing false that you are happy with.
I actually have the same issues as you. I have 3 boys and they have their friends over. I actually have my pond placed directly under one of the four large oak trees on the property. It's not that bad.
My boys are well behaved and well mannered and understand that they better stay away from the pond. There were some mishaps in the first year when they put stuff in the water and that first winter when they dumped many of the decorative boulders into it because they thought it was dead and I didn't want it anymore.
BUT, a couple of incidents that I know if I had talked about it with them before hand, they wouldn't have done it. Their friends also know they better stay away and if I catch them misbehaving they will be sent home immediately.

The kids LOVE the pond! I let them help me plant around it and we add a bit more every year. Today they helped me plant "their" flower seeds and they got really excited when they saw the hostas poking up out of the soil that we'd planted last year. They take great pride in the pond now, and will scold their own friends for going near it. When I'm out their and they have my permission, they like to show it off to their friends. They each "own" one of the goldfishes, and we have a bullfrog living in there now that they get excited to see.

My pond is more enjoyable to me because of the kids and it gives me something to share with them.

The oak trees are another thing. On one hand, they make the water slightly acidic from the leaves that drop in and stew. But the fish really like this. I go out once a week and clean it out with a net. It's relatively small so it's not a big deal. Every Spring I scoop out the leaves and muck, just as I would if the pond were on the other side of the yard. I don't think the job is any more disgusting (or oddly satisfying) because of where it's placed.

Anyway, you know what you want, not trying to talk you into something else. Just felt like sharing my experiences. Good luck with your project!