Even if a couple having been living together for several years and have children they are not regarded in law as common law husband and wife and if things do not work out a cohabitee will find that they do not have the same legal rights or safeguards as a husband or wife.
However you may be lucky as I take it from your posts you are in Scotland - the law is different north of the border. You may find yourself married under Scot's law even if you have not gone through a formal ceremony - but beware!!.... Under Scots law, there were several forms of "irregular marriage" (including marriage by correspondence), but all but one of them was abolished by 1947. Today, Scotland remains the only European jurisdiction never to have abolished the old style common-law marriage or, as it is known in Scots Law, "marriage by habit and repute". This type of marriage can be difficult to prove. It is not enough for the couple to have lived together for several years, but they must have been generally regarded as husband and wife, e.g., their friends and neighbours must have known them as "Mr. and Mrs. So-and-so" (or at least they must have held themselves out to their neighbours and friends as Mr. and Mrs. So-an-so). And it is a form of lawful marriage, so that nobody can say they are common-law spouses, or husband and wife by habit and repute, if one of them was legally married to somebody else when the relationship began.
Of course you could just get married...
