All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no harm for the mother to kiss her child before leaving for work, and there is no harm for her as well if she slips away without being noticed by the baby, but slipping out of the house is more lenient for the child and it is better. What is important is that she leaves her with a trustworthy person who would take care of her while she is absent. For more benefit, please refer to Fatwa: 83607 about the ruling and preconditions for a woman to work.
Allaah knows best.