It's pronounced roughly as "bay-bee".
You can also use other words depending on the context:
* رضيع (riḍīʿ) for a newborn baby
* طفل (ṭifl) for a young child, including babies
* صغير (ṣaġīr) for a small child, including babies
Remember that the pronunciation of Arabic words can vary depending on the region and dialect.