Hello and welcome to hcm forum,
If your cousin's baby teeth is shaking,it has to be removed.
If left untreated ,the tooth will become firm again and will result in eruption of permanent successor of the tooth lingually/buccally.
If the tooth is not able to remove by yourself,please do visit a dentist
Remaining baby teeth also has to be removed at the proper time.
Take complete course of medicines prescribed.
Meanwhile warm saline gargle can be done.
Brush and floss your teeth daily.
Please do get dental check-up in every 6 months.