M.P.
I do have the trailer and while it is good to take both kids--I have a 4 and 2 year old--
They don't like to be covered like that. But, if we roll the cover down, they get dirt all over them from the back tire. On hot days they don't want to be covered up like that.
you also need some expertise and time to set it up.
Looking back I wish I had got the bike seat--the ones where it goes in front of the rider look safer than the ones where they sit in the back. Also, as long as you stick to paved roads or non hilly roads it should be safe. Put knee pads on them and helmet, though!
plus, my daughter will be riding her own bike soon!