Hi, my name's Jim and I live in Scotland. Got three son's and a great wife (read as patient

).
I have absolutely no idea where to start with land sailing! All of the beaches near me are a very fine soft sand (only hard area is when the tide is out). I want to
build a landyacht with my eldest son.
I've had a good look around the forum's here and googled till I'm blue in the face. Almost all info I can find on building a landyacht refers to what I presume to be racing class types. Also searched for a good while for the fallshaw wheelbarrow rims suggested on here, most of my finds I can tell are unsuitable and others I'm not so sure about.
Here's what I'd like to build:
-scavenged/salvaged materials
-use as cheap a sail as possible
-provision to Safely seat a small child between my legs
-useable on soft and hard sand (is this possible?)
-something with brakes, I think I'll need them

ANY IDEAS??
Also, Is it easy to learn how to use these 'craft' (don't know what to call them)
Any and all advice / constructive criticism welcome
Thanks in advance. JIM