Allen, go buy a few lawn spears at the local renfaire. They are blunt but fun stuff. A kid may be able to throw them but the weight in the front might be too heavy and unbalanced. Or you could cut some bamboo and throw it in the yard.
I was given a knife around 4 and it was actually a dull, rusty knife but I prized it. I was given some sort of swiss army knife around 6, I think and held them, played with them, sharpened them, etc throughout my years as a kid with grandpa. I eventually was in scouts as well. I also was given a Japanese bayonet that served well as a sword till I got way bigger.
Watch them with the fire. My cousin and I set the backyard on fire when we striking a big piece of flint with a hammer. We put it out with the hose but looking back it was pretty dumb. Actually, it's funny as hell to remember though we freaked. However, scouting had prepared us for that so we stomped and kicked the dirt besides the hose. It wasn't very big.
I'm a big proponent of getting boys into judo before they are 6. Mainly because my dad did that to me because I was going to be a runt like he was besides him being judoka. He actually never thought much of karate/kenpo because he thought it made the kids too cocky instead of more humble in judo ( more physical contact, especially with the ground ). I never liked punching anybody in the face. Besides it leaves tell-tale signs of a fight versus a good punch to the gut or choke. Those also end schoolyard fights very fast. I don't think we wrestled in scouts and besides I could never have gotten my cousin to help me with that merit badge or patch.
Our treehouse had chains I hung off the branches. I don't think we had any rope around.
I took swimming before I was in preschool, I think but what really made me good at swimming was the whole thrown into the pool method. Since I went under, I just kicked and swam underneath the surface till the edge. I wasn't very happy about it but did realize swimming under the water was terribly easy and less frightening. I eventually taught 2 of my 3 brothers to swim underwater really easily.
As a kid, I had lincoln logs, legos, constructor sets before we got into some electronics and radios in scouts and afterwards I got to tear apart stuff my grandpa would find. Fun stuff.