The issue of the testator’s child who dies before the testator can take over the share.
Section 23 of Wills Ordinance, Cap. 30 states :
(1)   Where-
(a)    a will contains a devise or bequest to a child or remoter descendant of the testator; and
(b)   the intended beneficiary dies before the testator, leaving issue; and
(c)    issue of the intended beneficiary are living at the testator’s death,
then, unless a contrary intention appears from the will, the devise or bequest shall take effect as a devise or bequest to the issue living at the testator’s death.
(2) Where-
(a)    a will contains a devise or bequest to a class of persons consisting of children or remote descendants of the testator; and
(b)   a member of the class dies before the testator, leaving issue; and
(c)    issue of that member are living at the testator’s death,
then, unless a contrary intention appears from the will, the devise or bequest shall take effect as if the class included the issue of its deceased member living at the testator’s death.
If the testator has no will, section 5(1)(a) of Intestates’ Estates Ordinance, Cap. 73 states :
(1) Where under this Ordinance the residuary estate of an intestate, or any part thereof, is directed to be held on the statutory trusts for the issue of the intestate, the same shall be held upon the following trusts, namely-
(a)    in trust, in equal shares if more than one, for all or any of the children or child of the intestate, living at the death of the intestate, who attain full age or marry before attaining full age, and for all or any of the issue living at the death of the intestate who attain full age or marry before attaining full age of any child of the intestate who predeceases the intestate, such issue to take through all degrees, according to their stocks, in equal shares if more than one, the share which their parent would have taken if living at the death of the intestate, but no issue shall take whose parent is living at the death of the intestate and is so capable of taking;