Hmmm....well now - this could open up a can of worms, couldn't it? I mean - okay you've been together for 7 years and I'm not even going to mention the seven year itch - assuming that it doesn't even really exist. You have two children, and Lord knows - they're expensive little critters.
Like others have said before me "marriage" is just a word, and the ceremony is just a formality - and although it signifies and symbolises togetherness forever, commitment and true love - we all know that marriage is no guarantee of living "happily ever after".
This is not to trivialise the sanctity of marriage to any degree. But therein lies the difference between men and women. Men believe that if something isn't broken, why fix it - whereas women like to fix it, fix it, fix it, oops broke it.
But my summary answer to your question is this: you have been in a relationship for seven years - and the whirlwind earthmoving emotions have probably subsided a little for both of you, especially with two children. Your husband is probably wondering what happened to that "honeymoon" period, as are you - and you're probably trying to pin down a wedding so that you are reassured in your relationship. I understand both points of view - but I agree with the notion that a big expensive wedding, does not make the relationship any more committed or concrete than it already is.
Count your blessing my friend - you have a partner who loves you, and two adorable children.