As above, wife then kids and consider scenario where you are all gone (eg car accident/plane crash). You should think about a guardian for the kids and what happens to the money in that case. You will need an executor in the different scenarios. You and your wife should both make a will. IMO its worth paying a solicitor and also registering the will with the probate office
We got a will shortly after my son was born, but mostly so that my mother-n-law has no say over what happens to my son should the worst happen! We got some really good advice from the solicitor and he wrote it in such a way that it still applies if we have more children and will apply until one of us (wife or I) pop our clogs!
As above, go to a solicitor and get proper advice. Be prepared to be asked questions re what happens if you split up and remarry etc as well. Did ours so that it should be fine regardless of number of kids etc