This is the 1557th most frequent Russian word.
рады
"Рады" means "glad" or "happy."
The word 'рады' in this sentence expresses a state of happiness or delight at seeing someone, used with a subject in the first person plural and an infinitive.
Мы рады вас видеть.
We are glad to see you.
Here, 'рады' denotes contentment or joy concerning the receipt of a gift, agreeing in plural form to the subject 'дети' and showing an emotional reaction.
Дети рады своему подарку.
The children are happy with their gift.
In this sentence, 'рад' (masculine singular form of 'рады') expresses a feeling of pleasure about someone's arrival, used with a singular male speaker and introducing a subordinate clause.