The 70-year-old man approached the 21-year-old woman at a supermarket at Westfield shopping centre in Burwood about 2.30pm on Tuesday and helped her place grocery items in her shopping trolley.

He then allegedly insisted on pushing the baby's pram to the woman's car when they baby began to cry, police said.

Police said the woman became uncomfortable with the situation and went into the parents' room at the shopping centre, both for help and to feed the baby as it was feeding time.

The man then allegedly followed the woman into the parents' room and indecently assaulted her, police said.

He left as a man and a woman walked into the room, police said.

Police last night arrested the 70-year-old Burwood man and charged him with indecent assault and common assault.

He was given conditional bail and will face Burwood Local Court on July 9.

Police wish to speak with the man and woman who entered the parents room.

They can contact Burwood police via Crime Stoppers on 1800 333 000.