I think there are many women who would consider their love of their husband equal to that of their children, but in an "apples and oranges" way - different types of love, so much so they can't be compared.
That said, yes, it's frequent for women to love their children more than their partner. It's also common (and in my opinion, how it's supposed to work) for a parent (whether mother or father) to place more value on the children, which is different though intertwined with love. I guess I'll address the latter first.
While you dearly love your partner and chose to spend your life together, a husband is a grown man who can (generally, unless something terrible happens) care for himself. Whereas children are the parents' absolute responsibility. You *owe* your children love and value and care by choosing to become their parent, be that through adoption or biologically. Biology is also a big factor: the child is someone that the mother (and father) created in many cases. Creating sure beats falling in love! Though - back to the "love" issue - that's also a major role in all this: your child is half your romantic love's, even if not biologically (you still took on the parenthood role together, the child will still develop from his nurturing, and so on). It's like double the love, for the child as an individual and for the connection to the husband!
Furthermore, we're also biologically driven to protect and nurture children. They are our future, if you'll forgive the cliched expression. From a religious perspective, children are one of God's greatest gifts. Psychologically we see children as innocent and are often easily capable of seeing them in a softer light, or holding onto more patience with them, than with other adults around us. This may very well be because children often are not innocent little angels and we would otherwise be driven nuts by them! ;-)
Anyway, I'd like to add that I don't think a child (at least a grown one) should automatically come before the husband. All relationships should be valued. If, for example, a grown "child" were to intentionally and cruelly pose a danger to a woman's husband, I would expect her to side with her partner.
But ultimately there are so many factors beyond emotion (I'll let someone explain that amazing bond and jump into that depth) that cause women to love their children more: biological, psychological, spiritual, evolutionary instinct, and so on.