Making a Will is not about wealth it is about making sure that what you want to happen to your estate does happen. It gives you the opportunity to specify such things as who will administer your estate, who will care for your children and who will receive specific items of your property.
Adopted children are regarded as children of the adopting family for all succession purposes. In essence, an adopted child is treated as if he had been born into the marriage. At the moment of adoption he loses his right to inherit from his birth family.
However, there are saving provisions for rights that have already arisen.
Issue and descendants
The words 'issue' and 'descendants' are often found in home-made wills. Their legal meaning goes beyond your children and includes, grandchildren, great grandchildren and so on.
For the sake of clarity, these words are best avoided. If you wish to benefit your grandchildren, it is better to say so in a gift separate from the one to your children.