Basically, if one parent is British and born in the UK eg a British citizen otherwise than by descent any child born outside the UK should automatically be British by descent, when that child grows up if that child has children born outside the UK, they will not automatically be British. if they are born in the UK they will be, but if they are not there are other ways they can become British.
but if you mean only your first child can be british, not true, there is no number or limit,