Ответ:

1. Some children are singing "Happy Birthday" (It's a birthday party)

2. A girl is taking part in a competition. (It's a sing contest)

3. A boy is cooking food. (It's a barbeque)

4. A girl is getting presents. (It's a birthday party)

5. A boy is wearing a costume. (It's a party)

6. Some children are sleeping on the floor (It's a sleepover)