Obviously you can only leave what you own often a property has been disposed of that is named in the will so it has no effect. If you intend to leave your estate to your three children this is no problem but make it clear how you wish it to be done, make sure there are two witnesses to your signature who are not beneficiaries in your will,
It will not matter if they predecease you, but what happens if any of your children predecease you?
As has been said you may wish to consider life assurance.
It will probably be a good idea to name the beneficiaries as executors, but make sure they are aware of the location of the will and get their agreement to be executors, do make your will clear, if in any doubt get a solicitor to draft your will. A judge in the high court once said about a DIY will “the testator filled in the will form and signed it no doubt thinking he had done a good job, he had for the legal profession”.