English question:

1. 現在很少用 although 了，多數都是用 Though

2. 應是 Kelly and I，不是 Kelly and me

3. 不論是否單數還是多於一，禮物應為 Presents 而不是你最後的那個字 present. 還有是你可以用 one 來代替 最後 presents 的那個字．

4. 還有的是整句應該用過去完成式．

全句是: Though Kelly and I had bought tiny presents, Simon had bought a huge one.

句子沒錯, 但倒轉來寫更好.
Simon bought a huge present, although Kelly and me bought small presents.
although 可用yet, 則更英語化:
Simon bought a huge present, yet Kelly and me bought small presents.

Although Kelly and (I) bought small presents,Simon bought a huge present