1) Take your mom with you. Husbands are helpful, yes (at least, mine is) but extra time with grandma is special for the kids. This means they're asking HER for stuff instead of always asking me.
2) Go to a house where there are kids often. My kids where in awe of the number of toys they had to choose from. Also, things were pretty much kid-proofed.
3) Stay with family members who think your kids are adorable. We stayed with my grandma and both my mom's sisters who all share a big house together in southern California. I'm not sure how many times someone told me my kids were darling but you know what? It never got old :) Also, every time I turned around someone was feeding my kids whatever they wanted-- less responsibility for me!
4) Have older kids there for them to play with. Alright, this is probably not within your control, but it still made my vacation better. My kids got to play with some of their second cousins, all of whom are several years older (two 8 year olds, two 6 year olds) and it was great. Not only did we not have to worry what was going on with the older kids watching out for them, Kalena was thrilled every time she got to play with her "best friends" as she called them.
5) Don't plan anything. We went there with the sole purpose of visiting family and that is exactly what we did. Visited with family. It was great. No long drives to outings, no worrying about where or when my kids would nap, no expensive day trips that the kids won't remember. I highly recommend this method of vacationing.
Vacations like this leave plenty of time for the good stuff: lounging around.
That's the way vacations should be.