first and foremost, he has to be able to carry his hammock rig! so i made this pack for his 5th birthday. It's Xpac, like generic Dyneema I suppose, and is about 1600 cubes and weighs 6.8 ounces.
big enough for 2 quilts, hammock, and we will share a tarp.
the straps are 1/4 ccf filled and top straps are silnylon, along with a sil xtension collar.
oh, and hidden from view is the bottom made of 4oz/yd or so waterproof nylon (cordura maybe?)
next he'll just get a standard te-wa quilt, which on him will be full size, and a tiny TQ with 2 drawcords, so he can grow into it.