I always did this for valentines days with the kids. As you know dinner out is always so crowded and extra expensive that day, plus you'd need to pay a sitter. So we liked having fancy dinner at home for the four of us. This could be done easily for an anniversary.
I would set the table pretty; tablecloth, nice dishes, fancy wine glasses (for the kids filled w/ pink soda), combinations of flowers, petals, candles and wrapped chocolates. I never spent much on it, used what we had on hand. A little gift bag, filled inexpensively on each plate.
Had them clean up and dress special for dinner. They were always excited to participate.
I would make a nice marinated beef that you serve sliced (a tri-tip or london broil), DH would throw it on the bbq. Serve it with a baked potato and a small easy salad or steamed veggie and maybe bread. Heart shaped brownies (from a mix, used a cookie cutter) dusted w/ powdered sugar or a brownie sundae. Not to challenging of a meal for the cook, since it's her day too!
I always believe an occasion is what you make it, the special touches and effort. My kids still remember those special nights!