Need to ask if the child has any noisy breathing or snoring episodes while sleeping. If not it could be just nasal congestion.
Next Steps
1. Keep the child hydrated , give plenty of fluids
2. You can try nasal saline drops twice or thrice a day
3. Check if the child has some allergies or not, could be a case of allergic rhinitis ; family history could be helpful
4. consult a specialist
5. Try humidifier in the room
Health Tips
Consult a physician on emergency basis if anything of the following happens
1. bluish discoloration
2. child getting lethargic
3. Refusal of feeds