"I never said fulltime mum differentiates me from anyone, except that if I say that - whoever I'm talking to then knows that I'm not employed and of course it would tend to be - what do you do? and I'd usually answer, oh I'm at home with kids or something along those lines I wasn't being funny about it at all, just genuinely, I don't have a job title because I don't have a job, so what do I describe myself as?"
Technically, you are unemployed. 
Un means not so to say that you are unemployed, means that you are not employed. Contrary to your earlier post, it does not mean that you are looking for a job (usually referred to as job seeker), it just means that you don not have a job, which you don't ... so you are unemployed.
I object to the term 'full time mum' because again it is inaccurate. Being a mum is not a job role that you switch off at 7pm when the child goes to bed, or if the school phones to say your child is sick, you can't reply "Sorry, I'm not on duty now - my shift doesn't start until 3pm". You can't 'turn off' being a parent, as previous posters have said, it is not a job title. You cannot be a mum part of the time. All mums are full time mums, whether they work or not - so to say that you are a 'full time mum' is a meaningless statement.
Furthermore, what do these so called 'full time mums' call themselves when their children go to preschool or school? Do they then downgrade themselves to part time mums? After all, they are no longer there 'full time'! So I ask you OP, when your child starts preschool / school - will you be happy calling yourself a part time mum then, because calling yourself a full time mum would be terribly inaccurate!
Although, the only ones that get my back up are the mums who bleat on about being 'full time mums' and 'not leaving the kids' etc but then hold very part time jobs (in shops of an evening / weekend etc)... I know a couple who do this, but I work school hours (eldest at school, youngest at preschool), so these so called 'stay at home' or 'full time' mums actually spend less time with their children than I do with mine.
Apart from that, I don't mind - so long as it is accurate!