Brief Answer:
Ear examination needed. Antibiotics likely to be needed
Detailed Answer:
Thanks for using the Ask a Doctor service.
I have gone carefully through your query and understand your concern. Rather than putting olive oil, there are other fomulations available for cleaning ear wax (eg. Ceruclean Drop) which I will insist you to apply three to four times a day for the next few days. Since there is a bad smell, the ear needs to be examined and antibiotic drops like Ciplox Drop (can also come as eye drop, but it is the same thing) four times daily in the ear for the next 4-5 days. You might also need to give steam inhalation to the child.
I would strongly insist you to visit an ENT doctor to get the child evaluated.
Regards