I agree that an xtra is quite a tank to have as the only bike to do everything with.

I also agree that 4 weeks is maybe a little short. I believe in punishing myself with owning something I don't like, if I buy something I end up not liking. (In theory the punishment will help me not spend money unwisely next time?)

However, I think it is quite possible that the cargo cycle is overkill. Almost all people that do touring, do not use a cargo bike, so it is definitely not necessary for that. It is cool that you can carry a bike on your bike, as well as (multiple!) kids, but as you mention, it may be possible to find other ways. Of course for towing kids the normal solution is a trailer (which would also serve very well for towing groceries; not sure about a little kid's bike!)

So keep thinking about it, evaluating, and make an informed decision.

A thought: if you bought the cargo bike from a local lbs that carries Surly, maybe give them a call and tell them you think you're regretting your purchase and are maybe interested in a different bike. Maybe they can swing a deal for you to minimize your loss, take the cargo bike back for a certain percentage off, and/or give you a good percentage off a Surly?

Bottom line, I enjoyed reading about how you're using bikes with your family, I bet it's super fun for the kids, and healthy for all of you to get active, and progressive to be thinking about how to not be a family of Car Clowns like most of the rest of the US. Keep up the good work, and realize that no one bike is 100% ideal for all uses, but all bikes are at least somewhat suitable for all uses, and with perseverance you can get the job done!