A friend kindly offered to lend us their tub of kapla planks today as Harry had been playing with them for our whole visit. He has spent the rest of the afternoon playing with them too. They are smooth, perfectly straight-edged, perfectly same-sized blocks that can be stacked to form some great structures. There is an interesting section on the website about the play value of the planks and they are really well suited to Harry's freestyle creativity and engineering brain.
He built a pretty tall tower
Almost completed a boat following the inspiration guide
Peter was, unfortunately, a bit too interested and drove a car over the boat causing a collapse before making his own little ramp with the blocks
Enjoyed some balancing
And built a train track
I have just been in to tidy the playroom and have found the blocks neatly stacked and this truck packed ready for tomorrow. I think there may be some more creations! There are videos on YouTube too so I will show him some of those.