I've seen a picture of a bathroom with coloured lighting in the floor, which I'm interested in recreating at home. Do you know of a supplier, and is this lighting really safe for the bathroom, as I have a very inquisitive two year old?

I imagine you saw fibre optic lights rather than halogen, which, although they run on a safer low voltage, get very hot. Fibre optics are perfectly safe for wet areas like bathrooms and also outdoors, because the actual light source can be housed out of harm's reach, many metres away. All that's required is to route the fibre-optic ropes (which are just like a tube that the light is piped down) to where you need the lighting, and then cap with the finishing lens fitting.

Be warned: colour changing lighting can be more disco than spa if not done professionally, so sticking with static colours is recommended. The positioning and the installation still need to be well considered and competently carried out, so don't rush into fitting this type of lighting just on a whim.
Good-quality fibre optic kits can be bought online for around £400 through Unlimited Light.