give my grandson/granddaughter a present to celebrate his/her admission to his/her new school
「入学」＝ admission/entry to a new school/university
「祝いを贈る」＝ give a present/gift to celebrate ～
「孫」＝ grandchild, granddaughter（女の子の場合）, grandson （男の子の場合）
「孫に入学祝いを贈る」＝ give my grandson/granddaughter a present to celebrate his/her admission to his/her new school
「入学祝い」は、congratulatory gift for ～でどうでしょうか？
congratulatory 祝いの
gift 贈答品
congratulatory gift for entering ○○ ○○入学祝い
○○・・・ preschool, elementary school, junior high school, hight school, college, university ...etc.
「孫に入学祝いを贈る」
I'll send a congratulatory gift (for entering ○○) to my grandchild.
イギリス 
アメリカ合衆国 
