I can see the house being sold/remortgaged for ridiculous reasons and that there would be nothing to pass on.
Support that after you die, your husband's job relocates? Suppose that after you die, one of your children falls ill and it's necessary to buy an adapted bungalow? Suppose that after you die, your partner kindly offers to merge households with your mother so that the children can be raised better by both families, but can't?
I am more than happy for dp to stay in the house with them
Without a will, that isn't certain. It depends on what the trustees (if you are intestate, the Court of Protection) decide is in the best financial interests of the children once they reach eighteen. They are not responsible for ensuring that the children's homelife is beneficial, just that the investment makes the best return.
and that money from insurance & savings is to be used for them
Without a will, it can't be: it'll be in trust, and unless that trust has an explicit provision for its use for their education and maintenance, the money's tied up until they're 18. So if your partner wanted to, for example, be a SAHF for your children, he can't. If your partner lost his job, they can all live on benefits while looking at the money via the medium of bank statements. I doubt that's what you'd want.
I also assume that were we to marry that he would then have spousal rights to the house
Consult a solicitor. It's not as simple as that.
If you don't have a will, however, all your assets will be unavailable for any purpose for your children (education, ponies, cancer treatment) until they are eighteen. I don't see how that's a good thing.