Can I fit panniers, a child seat or kids trailer to an electric bike?

Panniers are fine. Providing there is a pannier rack! – If you notice the electric bike you use does not come with a rack. We have them available as extras in our accessories section.
Child seats are only suitable for some of our bikes. You May want to check with us first. Basically it depends on whether there is clearance at the top of the down tube for the seat post. A lot of batteries are positioned here so if they are too high, there is no room to get the clamp round. (Gepida and the few IZIP Models with batteries mounted on the rear rack are fine)
Kids Trailers are fine. And a lot easier to pull!