Royal icing consistency is tricky to determine, but here are my top tips.

The icing will look too loose at the start, but it thickens as you whip, so
don’t adjust until the end of beating. Think of it like a meringue, where egg
white and sugar gets thicker as it’s whipped. If the icing is very dry, add the
tiniest half teaspoon of extra water. If you’ve added too much water, add
more sieved icing sugar. Sieve everything, lest a stray sugar lump or lemon
pulp/pip block your piping bag later. The icing recipe will yield a little more
than you need, so go wild with the remainder or discard. Keep up to 2 days
refrigerated, and stir to re-emulsify before using, as it separates a little.

Food safety note – yes, this has raw egg white in it, but the huge amount
of sugar makes it hard for bacteria to thrive. If this still makes you nervous,
use pasteurised egg whites from the fridge or freezer section of your
supermarket.

Scrape the icing into a piping (icing) bag and snip the merest tip off
the end (or fit a #1 nozzle onto the bag before filling). Twist the bag
so the tension is tight. Clasp your hand around the twist in the bag – if
you hold it lower, the icing will be forced out the opposite end of the
bag, making the bench and your hands and your life messy.

Pipe the icing onto the biscuit, keeping the tip close to the biscuit.
I like a concentric circle of icing, mimicking the mesmeric spinning of
a hula hoop. After icing each cookie, twist the bag again to keep it tight.

Allow the royal icing to cure (harden and dry) uncovered at room
temperature for at least 2 hours (overnight is best) before packing
into an airtight container.

Adaptrix
You know, for kids
Omit the pepper from the German
gingerbread spice, and the fresh
and candied ginger. You can even
dial back the spices and shorten
the bake time so they are less crisp
and more of a kid-tooth-friendly
hardness.

Go dark
Instead of golden syrup or honey,
use treacle or molasses. Just swap
the dark muscovado (brown) sugar
for light brown sugar.