Do you or your hubby have access to a group legal plan through work? If so, getting this done will be super cheap. It's like an HMO for legal issues. We used Daniel Levy in Lincolnshire through Metlife group legal plan.
Make your wishes known NOW about who should be the guardians for your children. Get their commitment for that responsibility. You can rest easy knowing that the right people will pursue whatever is necessary to fulfill your wishes in the small chance that something bad happens before you get things in writing.
Side note: be prepared to tell who will be power of attorney for health and financial concerns.