Fencing in front of stream

I would suggest post and rail with concrete posts with either wire infill or Pickett style fence

I would put a picket fence up with the round top and the panels are already made use good 4x4 posts concreted in then you get a good solid strong fence for safety but can still look out into the country

I would suggest a chain link especially in black as it would be easy to see through

I would use a 6x6 trellis fence so still can look through it and kids are unable to get through were still able to put some nice hanging baskets on it

I like your idea but have you considered privacy panels

Use 4x4 concrete posts with criss cross ranch style fencing with child proof green plastic coated wire inch x inch to prevent putting arms through

I'd do a 4' pointed top picket fence and set the pales, the vertical bits, as close together as necessary so that the children can't climb it by putting their feet through to climb up rails. Depending on the ground, either concrete in the posts or use 'Metpost' type spikes. You can use 3" posts if you want to, if nothing else is going to be pushing against it, there's no need to use huge posts. I have made fences like this with 3" posts concreted in to 2', 3" x 2" rails and 4' pales and they have remained stock proof (cattle proof) for years and I guarantee my work for 5 years and never had a call back in nearly 30 years.