Not embarassing at all. I can't think of any of my friends or myself with kids who don't have this struggle from time to time. Here's my thoughts on the subject.
Maintaing a healthy sex life is as important if not more important then anything else you do in a given week. That doesn't mean you have to be putting it out there every day but you do have to make it happen. It just takes a little more effort but it's worth it.
Now it will be me a bit embarassed but you asked! It's not quantity but quality! No a quickie isn't going to do much more then give him a release and sex should be more then that. You should BOTH enjoy it and the phsical part of your marriage enriches every other area of you union.
No, you are not always going to be in the mood and no it's not always going to be earthshattering but there are a few things you can to do help facilitate it and make it what you both want and need.
Think sexy! So what that your 3 year old just pooped on the floor and your 4 year old tossed it at the dog! Find moments in the day to do some fantasizing. It's as simple as just thinking about your husband and how happy he makes you and what naughty things can you think of to make HIM happy when he gets home. Keep that up when you can and you'll find yourself anxious for the kids to get to bed already!
Dress to impress. So your day consists of a target stop and maybe a park playdate. No reason why you can't put on your skinny jeans a cute top and sexy shoes right? I bet you get some flirty looks throughout the day and what an ego boost that is! When you feel pretty your much more likely to be a little more aware of your looks and your impact on those around you. It feels good to be noticed and to remember how lucky your husband is to have you!
Watch your husband. Don't just see him in your peripheal vision. Check him out! What about him just does it for you? Is it his butt? Is it a crooked smile or a sexy voice? Figure out what he has that pushes your buttons and focus on those features when he is in your presence.
Touch eachother. Foreplay can last all day if you do it right. Maybe a little longer/deeper kiss before he leaves for work. Maybe a phone call that's short and sweet but a little racy??
Excercise! I never feel more sexy and in the mood then I do after a workout and a warm shower! If your active maybe a jog around the block with the kids just before he gets home/kids go to bed. Gets your blood moving and will at least temporarily get rid of that too tired to move feeling at the end of the day. Just be careful to avoid excercising just before you go to sleep. (Well CERTAIN excercising. ha ha)
Ask him to make you feel wanted. Tell him that you need him to seduce you. Tell you he thinks your pretty, how much you turn him on etc. And keep the groping to a minimum. I hate that when my husband does that. Nothing turns me on less then him reaching out and grabbing me in the middle of making dinner or vacuming. Your husband can do a lot to make you feel like putting more of an effort into sex.
Do it when you don't want to. Fake it. I know, probably not PC to say but I know there were times when I just "wanted to get it over with" and went through the motions. I will say though that by the time it was all said and done, I found myself getting into it and enjoying it much more then I originally thought I would.
Hope these tips help! This is so common though. It's ok to go through periods of time when you just aren't connecting physically. Just don't let those last too long!