This is the 1479th most frequent Japanese word.
達
Pluralizing suffix; denotes a group or emphasis (e.g., friends, people).
In this sentence, '達' is used as a suffix to indicate the plural form and inclusiveness in '私達' (we/us), meaning the speaker and others together.
私達は一緒に映画を見ました。
We watched a movie together.
Here, '達' creates the plural form '子供達' (children), suggesting a group of children.
子供達が公園で遊んでいます。
The children are playing in the park.
In this example, '達' is added to '先生' (teacher) to form '先生達', pluralizing it to mean a group of teachers.