I can completely understand your problem - I've moved constantly my whole life, first with my parents and now with my own family, and it's hard to move from somewhere like Manila where your children have such a wonderful outdoor life with plenty of sunshine and swimming to somewhere like the UK!
My only advice would be to keep your children well informed and involved with your move. They're not going to see it as going "back" to the UK, as they've never lived there. To them it's a new experience and, by involving them, they can see it as a new adventure. That's the way it worked for me at least, moving around Asia as a child, and it's also worked for our son so far (again, moving around Asia and Europe).
Show them the flight route, get them to "help" with the packing, explain to them that there aren't many outdoor pools in the UK (and how the weather is very different to Manila) etc. - anything to make them think they're part of the move, which will also help to decrease their shock when you do arrive in the UK. You can tell them a bit about your childhood living in the UK as well and, if you have family and friends in the UK, you can tell them that they'll be able to see more of "Granny/Aunt Whoever/etc." that might help them look forward to the move. Remind them, too, that they can still keep in contact with their old friends in Manila and that maybe one day you'll go back there on holiday (by the time they've settled into their new lives in the UK and made new friends at school, they'll soon forget about Manila and won't hassle you to go on holiday there!). Also, if any of your friends from Manila are visiting the UK, you can easily meet up with them.
We moved "back" to the UK when I was around 18 and the first thing my parents did was take us on a car trip all around England and Ireland (I covered Wales and Cornwall later with friends from University and Scotland with my husband!). My brothers were around 16 and 9 at the time, so it was a great "welcome" for us, having grown up in Asia all our lives until then. Obviously your children are younger, so a big trip like this isn't necessary, but I just wanted to mention it as another way to decrease any shock of moving from a place like Manila to the UK.
Most importantly, don't worry about it! Don't make a big fuss, as your children might pick up on your discomfort. Just go with the flow and let them enjoy the whole adventure of moving and settling in somewhere new! When you have moved back, don't keep talking about Manila in a more positive way than the UK, as this could also affect the way your children settle in. (My mother was so unhappy the first year we moved back and her mood did affect us as well - now, of course, she couldn't be happier and wouldn't want to move back to Asia even if the opportunity came along!)
Good luck with the move and just enjoy it - at least you'll be moving at the beginning of the summer!