¨los ¨or ¨les¨

Question

Can anyone tell me why use ¨les¨ in these sentences'why not use ¨los¨?
1.---|Ellos creían que les escondía algo.(they thought i was hiding something from them).
2. ---|Al oír que queríamos ayudarles,las chicas se pusieron alegres.( when hearing i would help them, the girls became happy).

¡Muchas Gracias!

Answer 1

1) indirect object, les is mandatory

2) should be las (direct object) but les (it is called" le de cortesía") is permitted.