I will let some of the women pontificate on motivation etc here, but I will say this. The thought of potential interuption by a child during the act is a HUGE turnoff! At the risk of being offensive here, you have got to keep the kids out of your room! Mom and Dad's bedroom should be off limits any time the door is closed. That helps reduce the anxiety. If you are unable (cooperation from the wife) or unwilling (your own parenting style and beliefs) to keep them out through training, you need to keep them out physically with some sort of bolt on the door.
You can find a lot of postings on making the bedroom a more intimacy friendly place, from de-cluttering to motif etc, but being uninterupted during sex is rule #1.
