We did gingerbread house from Lidl - was about a fiver, but came with icing Santa, snowman and Chrstmas tree !
For cement: mix 1 egg white with approx. 350g (10-11 oz) icing sugar, v easy, use a few drops of water/lemon juice if it is not soft enough.
Piping bag can be made out of greasproof paper rolled into funnel shape IYKWIM.
VERY VERY IMPORTANT: for structural stability use cocktail sticks/tooth picks to stick the house parts together with icing as glue.
Leave over night. Icing will dry rock hard.
Then, and only then, let children anywhere near it .
Decorate as you will.
And of course you should jolly well eat it; what's the point otherwise??
We tend to keep it until Christmas, then take apart, if rockhard put into airtight tin/plastic container with a few slices of apple: after a couple of days, voila, soft delicious gingerbread with apple flavour!