Your right the red river is nothing to mess with, whether you are in a boat or standing on the shore. So your concern is warranted.
I have a 9yr old that I take out shore fishing on the red. There isn't really any spots that what I would consider safe. However in the spillway is probably a bit less dangerous although it still holds it's hazards specially if it is open and if water is coming thru.
The sure thing I can tell you is keep your kids in life jackets and keep a rope handy. This is so can throw a rope vs jumping in after him. Last thing you want is both of you in trouble. Heck I keep rope in my tackle bag always whether with kids or not. Go over safety procedures with your kids before you head out.
There is one spot that I really like for taking the boy as it is pretty wide open and a bit easier to control what is going on there. Plus the fishing isn't so bad either I will PM you some details.