My Dad felt the same way when he retired from work. He kept saying, now what do I do all day? That boredom lasted about two days until he FOUND tons of stuff to do--mostly things that he used to do before he got so busy with us kids that he didn't have time to do.
He exercises (runs/walk 5 miles daily), chops wood (for winter and for bonfires during the summer nights), is more active in the fire department, goes fishing, goes hunting, works out in the garden/yard, washes all our vehicles, goes camping, helps friends that are doing home projects and need help...basically anything and everything that needs done or that someone needs help with he does, just to keep busy!
I'm not sure if any of that stuff interests you, but I'm sure you had some sort of interest before you had children, and you could rekindle that or find a new hobby. Do you have grandchildren? Hang out with them--go to their soccer games or take them fishing and teach them something new. Learn how to cook if you don't already know how and make your wife dinner some night! Join a golf league or bowling league...I work at a golf course and a large group of retired guys formed a golf league in the mornings. Now, instead of playing once or twice a week like most leagues do, they play every morning. Since they walk, it's a great way to stay in shape, and it gives them something to do for a few hours.
Just a few suggestions...I hope you find something to do!