I made Sandbox with collapsable benches

I made Sandbox with collapsable benches

Finished product first!

I was searching for sandboxes on Amazon and came across one like this. I decided I should try to build it to save some money. I've never built anything before, but I figured I could give it a shot.
Parts List

(4) 2x10s cut at 46.5" (I used pressure treated for these ground-contact pieces)
(12) 2x4s cut at 48"
(6) 2x4s cut at 7"
(4) 1x3s cut at ~22" (see below for info)
(10) Standard Door Hinges (screws included)
(36) 3" Wood Screws
(20) 1.5" Wood Screws
Starting the frame

Used (3) 3" wood screws to create two L pieces for the frame. These were cut at 37.5" so when the frame was assembled it would be 48" x 48"
Frame assembled

I suggest not doing this down on the ground; not great on your back!
Trying to figure out spacing for the 2x4s

First 2×4 screwed down

First seat 2×4 attached

The first two 2x4s get screwed right to the frame. The third and fourth will be the seat.
All there hinges installed

Some more of that sweet folding action

Used a 1×3 to create the gap between seat 2x4s

Connecting the seat 2x4s

The two seat 2x4s get connected via these 7" cuts of 2×4 (I took out the middle one later in the building; wasn't necessary)
Seat assembled!

Losing light, better get the other side caught up

Other side seat finished

Whoops!

I put the outside 7" piece a little to far out. It kept the seat from folding into the frame
All better!

Both seats complete
Adding the first back support 2×4

The back support pieces are held onto the seat by two hinges
Lets keep it symmetrical

Getting closer!

Connecting the two back support 2x4s

Another 7" 2×4 is used to connect the two back support pieces
Ignore that 1×3 for now – just using it for stabilizing

testing out the unfolding/folding of the bench
matching the other side

Benches folded out

1x3s serve two purposes

These 1x3s help connect/strengthen the back support pieces. They also keep them from folding backwards when the bench is upright.
Back view of bench

Those 1x3s sit on the ground and keep the bench from falling backwards and being useless
Cutting the 1x3s

Since I was doing this all by looking at a picture of one on amazon, I had no idea what the measurements of these 1x3s would end up being. They were way too long at first, so I screwed them on, marked where the top of the bench came to, unscrewed them, tried to cut them with my $5 tag-sale-find circular saw which started to smoke from the motor and tripped a breaker, drove to home depot to get a hand saw, came back and cut them and screwed them back on. Fun!
Finished! Now I need someone to help me move it outside.

The pressure treated 2x10s made it too heavy to move myself.
GFilled with sand!

I bought 12 bags of play sand and 5 bags of pea gravel (for texture/playing/whatever). I thought it wasn't even going to be close to filling it but I only ended up using the 12 bags of sand. I might still add the pea gravel if I can't come up with another use for it.
Closed up

Should work just fine for keeping out animals, leaves and other stuff. The bottom is open so any water should drain into the ground. I'm worried about the 2x4s and 1x3s since they are cheaper wood. I'll probably water-seal it at some point before winter.