i would wake the kids up an hour earlier that day so they get tired sooner, put them to bed early and do a romantic dinner w/your SO. or if its just too late for you guys to eat, or you don't want to break any eating as a family rules, do a candlelit desert.
Oooh I like the candle DESERT idea lol that could get very fun for you two! Try to surprise him with it. After the kids are asleep or if they never sleep like mine, go rent ton of movies for them and when they are occupied set up. I would run a bubble bath by candle light first, then have chocolate covered strawberries and soft sensual music to accompany it. Have some yummy wine or shampange..I just tried one from walmart called Boone Farms, Strawberry Hill it was really cheap. Do some whip cream dip too and other fruits you enjoy. plan some sweet little sex games and walla a night for him and YOU to rememeber! GL happy anni!
I am kind of sentimental, so I would suggest making a timeline scrapbook of the past 5 years. Or even since you started dating. Do the dating, then the wedding, then the married life before kids, then the first child...so on and so on. Whatever you decide, Happy Anniversary!