I just don't fancy gaining weight, and the other thing I don't like is the slump after, when you realize you've cheated...hmmm I dunno
I think that's your answer right there. If you know that one evening is going to result in you feeling negative about yourself for a significant amount of time after, (and therefore potentially having a negative impact on your attitude toward the diet) then it probably isn't worth it.
I'm just not sure what to do. I'm a single mum, it's just me and my two boys, and for their dinner that day I was thinking either picky party foods or a pizza, fries and a milkshake deal from the lovely little pizza place nearby. It wouldn't be anyone else, so it's not some family function.
I don't have kids, but my Mum was (and still is) extremely overweight/obese though out my childhood. She was clearly unhappy, and those are the memories that stick with me more over what it was she did for me for any of my birthdays. I was a very active child, and my favourite memories (honestly) are of going for long walks on the moors or through forests and just running around till I plain knackered myself out. I can maybe remember one or two cakes from a couple of birthdays, but I can definitely remember my Mum watching me do active things rather than join in with me doing them (for instance, I
loved water theme parks, and for obvious reasons my mum hated them), and I never really understood why.
I've got to be honest, I think you've actually got the perfect opportunity here to do something completely different with the kids here that will stick in their heads for years to come. And it doesn't have to cost the earth, like I said, when I was 5 doing anything different to what I normally did was exciting. Horse riding lesson, trip to a museum, trip to the cinema... all of these things would have had me wetting my pants in excitement (unfortunately, probably literally - I was 5!).
Then at the end of the day cook him a "Special Meal" of something you know he loves but doesn't get very often. This gives you the chance to establish a yearly ritual, which kids love. In my case, Mum used to cook me a massive chinese every birthday from the ages of 8 to 15; it was the only time of year we'd have it, and I have very happy memories of the excitement of getting my "Special Meal".
It doesn't have to be about cake and sausage rolls - grab the opportunity to do something different! It'll be good for your kids, and I suspect even better for you, because it'll keep you on track to being the person you want to be, which will one day translate to your kids having lots and lots memories of a happy Mum when they were growing up.