With respect that isn't a simple will. If you leave everything to each other there is nothing left to give the children.
If you leave everything to each other with the proviso it must be passed on to the children you are creating a trust which means (without suitable wording to the contrary) that the surviving partner has no access to any money left by the deceased - only to the interest on it. The trust also takes administrative work to run - you may or may not wish to saddle your heirs with this.
So your first task is to decide what you actually want to do with your assets.
Having done that I'd approach a will writing firm (just google will writing) who seem to do it for under �100 or a STEP praticioner (
http://www.step.org/index.pl?n=2000;section=13 ) - maybe a bit more, but a bit more expertise and advice.
Don't go to a bank - they charge the earth, not for the will, but to administer the estate afterwards. Likewise with a solicitor - it may be better to pay a little more for the will that doesn't name them as executors than have a cheap one naming them which leaves your heirs no choice.