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As per the previous response, you need to check if allowed to keep pets. I would ask what size of flat you have and if you have access to a garden or park. If so I would suggest a smaller size of dog in which case you may be better getting a puppy as it will then grow up with your children and be used to them. Labradors while great family dogs need lots of walks and are quite boisterous even when trained properly, although they do calm down with age, retreivers are also good dogs.
On the smaller dog front West Highland white terriers, Bischon fries and the like are good dogs.
The main thing to remember is that a dog is a 8 to 16 year commitment and they become part of the family, worthwhile if you can persevere.