Hi @Bekkaj & welcome!
That image is an interesting one. It's really a classic case of how something that looks simple at first glance is, in reality, reasonably complicated in some respects.
I managed to find a higher quality version of that image & the equipment shown is in-fact not a pallet but a high-quality piece of purpose designed play equipment.
That’s not to say that pallets couldn’t possibly be used but with anything for kids you have to foresee every potential hazard.
First I’ll just walkthrough that image. The A-frame itself looks to be made from treated pine poles (if they’re round they’re poles if they’re square they’re posts) and then at the top of the frame they are held together with galvanised steel joiner-collars that also form a sleeve for the horizontal pole.
These upright poles are all concreted in.
The planks are a pretty straightforward board nailed or screwed on.
So all-in-all it’s a simple build however it is relying on those very customised galvanised joiner-collars.
This could be replicated with pallets however, getting back to the kid-friendly aspects, there are a few caveats.
It is no longer recommended, or in fact legal, to use CCA treated pine in any situation where regular contact, such as play equipment, occurs.
Many pallets are treated pine but won’t be labelled as such so you need to find ones you know are definitely not CCA pine or find hardwood (which is very heavy & harder to work with).
Pallets are rough. They are designed to be machine handled, not hand-moved, so you’d need to be doing a lot of sanding etc. and then find suitable slats to insert between the existing. You could likely do this by cannibalising a second pallet.
You’d also need to remove any sharp edges and corners.
You’d likely need to set poles in the ground and then secure the construct to them as you can’t really just concrete the foot of a pallet in (although I suppose you could set single-sided stirrups in the ground in concrete & then attach to these) but you could of-course have it so it’s mobile.
At the top you could drill and bolt the pallets together although the bolt ends would need to be covered somehow. Otherwise you could use concealed brackets or timber underneath or on the sides to form a joiner. Being an 'A'-frame design you'd need top & bottom braces to stop it spreading apart.
Personally, I’d build this one from scratch, not from pallets, mainly due to the issues with treated pine and making the pallet safe (i.e. splinters, hard, sharp corners). Unfortunately you do find a lot of ‘easy ideas’ on the web where the people posting them have never actually explored the issues of building it the right way or haven't been aware of some of the potential risks such as treated pine.
A lot of the play equipment parts such as climbing hand-holds and mini-cargo nets are easy enough to get. There’s a whole range of stuff here.
I should apologise too, don’t let my ramblings put you off. I just immediately look at it from the point of how it can actually be done the right way.
