I have made many different kids chairs and a few tables. This design wins hands down for both simplicity & longevity . No mortive & tenons needed ensures speed in construction but i found a square correctly sized box helped keep everything square during assembly. I had to incorporate routed grip handles for easy removal from the chair (without loosening screws).
The prototype was made in early 80's and has evolved with minor changes to make construction easier & quicker . I'm not sure if this new version will last as long as others before it, as I have increased the hole in the legs to facilitate better routing. Larger holes, like a half circle, in other designs allow timber to crack through the shortest part. I still use the stand on and wiggle test and as I am some 20kg heavier I think they will be fine.:lol.
The new one started when my son asked if I still had the ones he enjoyed 25 years ago & his sibblings there-after. Unfortunately I had lent a couple & they were not returned. I did still have one but he needed two. I decided to use the one I had as a template & now with tablesaw could realize improvements over the original which originally done with jigsaw, 3 wheel bandsaw & a table router.
I opted for an "outdoor" polyurathane but it was only available locally in full gloss (yuk). I still prefer a semi gloss or matt finish.Full gloss shows up all blemishes in the product as well as the finish (runs). I had/have probs with my compressor (1991 model) and the days were extremely humid at time of finishing but still ok with the end result (would not be for adult furniture but the kids will give 'em curry to crayons).
To keep it simple I made from Pine that was available DAR in the current size which is wider than the originals.
New screws are available nowadays for treated wood so I used those instead of original zinc ones.