We have three, difficult to say how planned or surprising it was at the time (7years back) but it's brilliant! The transition from 4 to 5 is a big one as the little ones suddenly outnumber the parental units. It kind of means that their world carries more weight at home, which is really good as they experience agency in their world. It's almost more like growing up in bygone decades where they'd band together and cruise around on bikes, finding their own strategies for dealing with being small and not always equal. Another thing is the question of space. Most families of 5 have less space than they might like meaning that there is a lot of sharing bedrooms, having to keep their stuff limited and out of each other's way. But these are great lessons in keeping your house in order before you start to take issue with the world beyond. Living a bit on top of one another also means they we all have to put the effort in to be both tolerable and tolerant. Group dynamics chop and change all the time. Naturally the wheels come off that trike regularly enough, but there's another great set of lessons for life going forward. On reflection, the intimacy it creates is just the most precious thing in my life so far. They'll be off on their own personal missions soon enough. In short; congratulations! Take courage. It is new territory and will shake things up unavoidably but as the dust settles you'll start to see many many more benefits to the larger family than cons. Speaking from some pretty hectic experience that is. Good luck!