Can’t really comment on your plan but I had to replace the same boards on my daughters Wendy house some time ago and I got boards (very similar to the ones you have posted) with fake grass stuck to them. They looked well and worked well. Might be something to consider.
Eldest had a tantrum and fucked the already precarious decking of the Wendy House.
Replacing with these seems like the easiest and acceptable option price wise.
https://www.wickes.co.uk/Wickes-Premium-Natural-Pine-Deck-Board---28-x-140-x-2400mm/p/101000
Product details
Length: 2400 mm
Thickness: 28 mm
Width: 140 mm
Material: Pine
Colour: Natural
Do people think a 1cm "expansion gap" on 5 boards will be OK? Or will it look a bit shit/pose a risk?
Cheers.