We have a lot of customers who want to put a childs seat on the back of a regular ebike. While this is entirely possible on most of our ebikes, it's not always ideal. The reason is that when you have a child on a child seat on a rack on the rear of the bike, there's usually nowhere to put all the gear that goes with a child.
Usually when you're picking up a child you've got a school or a crèche bag and various other things. You've also got your own items, which you might normally carry in a backpack or a pannier. A pannier will not fit on your rack when you have a childs to seat on it, so you end up having to put it in a backpack. However, if you put it in a backpack, and usually the child seats are so close to the rear seat that the child ends up having the backpack in their face. So that's not ideal either.
Ideally you'd spread the load front and rear so that you put all your own personal gear and the child's gear on a front rack. Now, that's not always possible on the bike that has suspension forks but on some bikes, it might be possible to put a fork mounted front rack. If you're putting a lot of weight on that it can make the steering a little bit unstable, which really isn't ideal when you've got a child on the back.
However, we do have a couple of workarounds for people who have an existing bike and child carrying systems. We have some little piggyback bags that go on the back of our child seats that allow you to put the child's bag, or what have you, in there without it flapping around. We know well the situation of parents trying to tie on backpacks to the back of the child's seat. So, the piggyback bags are a good temporary solution but I would say they're only a temporary solution. This is because they compound the issue of putting all your weight on the back, which can make the bike, more unstable. And so really the ideal way to carry a single child is to have a utility bike, that has quite a large rear rack that can usually carry a pannier alongside a child seat, as well as a frame mounted front rack (you can read more about utility bikes here). So unless you're wanting to go on only recreational rides with your child when you don't need to carry much stuff, this setup is a lot better for child carrying, as it gives you a lot more options and much more capacity.