Think of sex as the bonding glue that keeps your marriage together. It needs to be a priority for you too. Sex is invigorating, stimulating, and relaxing.
Try encouraging your husband to do some more things with the kids like baths, storytime and bed. Arrange for sitters or family members to take the kids for a few hours (Ice cream and the park or zoo or whatever).
Spend time thinking of how attractive your husband is to you and then act out your attraction to him. Get a lock for your bedroom door because sometimes you will need to lock the kids out to have a little private time with hubby.
Make certain your diet is balanced and you may want to take some kind of multi-vitamin supplement which will help increase your energy level too.
Your children won't always be little and if you really want to stay with your husband for a lifetime, lay it on him often and frequently. Please stop taking him for granted and show him you appreciate him as a husband and a father and as your lover and friend by making love to him often and frequently even though you might not feel like it. This may sound ancient but I know it really works.