US - always pay for upgrade and if the loads are tight you should purchase an upgrade ahead of time even if you don't want it. On short hauls, save it unless you need it to get on. Sadly first to Europe or on any long flight is hard to come by even if you have purchased the upgrade plus if you don't use the upgrade you have to mail it back for credit. So for Europe that can be money that you need in your checking account (especially if you are an employee). Still we keep them on hand just to have the wiggle room when we travel- both literally and figuratively. I have traveled many times with grandparents plus four kids- even to Europe. I couldn't afford the first upgrade for that may folks- but even if I could have nonrev children were not allowed in first at any price until mine were grown. Be prepared to sit all over the plane which means unless the plane has several empty seats don't attempt this with car seat, diaper kids- or even toddlers. However if you end up in a tight situation offer to buy drinks for someone to move. It works every time. Always check in early if you are flying with small kids. All of this being said- make the effort if you have kids they will be better adults for it.