小学三年级英语第一节的句子通常包括一些基本的问候、自我介绍、介绍他人、表达位置和方向、以及日常用语。以下是一些可能出现在小学三年级英语第一节课中的句子：

1. Hello! / Hi!

2. I'm [Your Name].

3. This is [Someone's Name].

4. Where are you from？

5. Welcome!

6. Good morning/afternoon/evening.

7. Nice to meet you.

8. How are you？

9. I'm fine, thank you.

10. What's your name？

11. My name's [Your Name].

12. He/She/It is [Someone's Name].

13. Let's make some cards for them.

14. This is my new friend.

15. His/Her/Its name is [Someone's Name].

16. He/She/It is in Class [Number].

17. Can you spell it？ [B-O-O-K, book.]

18. What's this in English？ [It's a book.]

19. I like playing with my friends.

20. My favorite color is blue.

21. She has a pet cat named Whiskers.

22. We are going to the park later.

23. He is good at playing soccer.

24. My mom makes delicious cookies.

25. The weather is sunny and warm today.

26. They are going on a family vacation this summer.

27. I have a new backpack for school.

28. The book I am reading is very interesting.

这些句子涵盖了三年级学生英语学习的初级阶段需要掌握的基本语言技能，包括问候、自我介绍、介绍他人、表达位置和方向、日常用语等。在学习这些句子时，学生可以通过角色扮演、对话练习等方式来提高口语表达能力。