Using 'Se' as a Substitute for 'Le' or 'Les'
When the indirect-object pronoun le or les is immediately followed by another pronoun that begins with an l, the le or les is changed to se. This prevents having two pronouns in a row beginning with the l sound.
Déselo a ella. (Give it to her.)
Se lo dijo a él. (He told it to him.)
No se lo voy a dar a ellos. (I'm not going to give it to them.)