Infant paracetamol (such as Calpol) is 100mg and is given in 5ml measure for a one year old.
Night Nurse has 1000mg per 20ml dose, so 5ml is FAR too much
I really wouldn't give him anything except for 'baby' stuff.
Ask your local pharmacist for advice.
The cold will clear up soon or if it doesn't, take the baby to the GP.