Hi
I was in the same situation as you. I was working full time (50 - to 60 hours a week), with a little boy since he was less than 2 months old. I was supposed to be paid 7 pounds net an hour, but as the parents were always 15/20 minutes late, I ended up working for less than £7 per hour.
I had a really good relation with the parents, loved the little boy.
But I couldn't help being annoyed by how little I was paid (I used to be paid £10 net per hour but it was a part time so I just thought that I had to accept less). And in addition to taking the little boy to activitie, I had to do all the cleaning, washing clothes and ironing (for the parents too), polish the silver, etc...
In January, I left the job, the parents were not happy. But I was killing myself for a bad salary. It took me some (stressfull) weeks, but I finally have been offered two jobs. One was £10 an hour with one family and the second one, a nanny share, £12 net per hour. I took the second one. I have started this week.
I miss the little boy, for sure. I felt guilty to leave the family, for sure. But I am happy I am not strugling that much with money. And I am already love the two babies i work with. And the families are also super nice. But they don't ask me to do so much.
I am sorry, but £7 an hour for three kids, with 7 years of experience, that is nothing. And I am sure you can find better (even if I have to warn you, it is indeed harder to get a good job well paid now than it was 3 years ago, it is true. But I am sure you can find something) (Oh by the way I live in London, I don't know for the rest of UK).
Being a nanny means that you get more emiotionally involved with the family. But I have realised that at the end of the day, it's a job. And I give the same amount of love/attention to the children wether I am paid £7 or £12.
Wow, sorry that was long. What I am trying to say is that you should think about yourself first. And if you can get a better job, with a better pay, you should take it. The family will find another nanny (And you can also just tell them that you either need a pay rise, or you will need to find a new job). And to be honest, does the family thinks about you when they pay you so little for so much work, with not a lot of breaks and no contract? I am not sure of it. ;)