My niece has a painless pea-sized lump in her jaw muscle and another neck now the one grown to quarter sized about 3 days but still What could this be?

There are several possibilities for what could cause pea-sized and quarter-sized lumps in the jaw muscle and neck. Some possible causes include:

* Swollen Lymph Nodes: Swollen lymph nodes are often caused by an infection or inflammation in the body, such as a cold, flu, or sore throat. They are typically painless and can range in size from pea-sized to grape-sized.

* Muscle Strain: Overusing muscles can cause a muscle strain, which is a small tear in the muscle fibers. This can result in a pea-sized or larger bump and may be accompanied by pain.

* Lipoma: A lipoma is a benign (non-cancerous) growth made of fat cells. They are typically soft, painless lumps that can grow anywhere on the body, including the jaw and neck.

* Infection: A bacterial or viral infection can cause lymph nodes in the jaw or neck to swell.

* Thyroid Issues: An overactive or under-active thyroid gland can lead to abnormal growths or lumps in the neck.

Since your niece has had the lumps for several days and one has grown to quarter sized, I would recommend seeing a doctor to determine the exact cause. The doctor will be able to feel the lumps, examine the surrounding area, and order additional tests if needed, such as an ultrasound or biopsy, to pinpoint the cause. This will allow for proper diagnosis and treatment.