The girls, aged 11, 10 and 15 months, were riding their bikes near Woonona Beach, off Thomas Collaery Place, about 4.30pm when they were approached by a man.

He briefly exposed himself to the girls before walking away.

The man is described as being aged in his mid-20s, Caucasian with tanned skin, of average build, clean shaven with short dark hair and between 170cm and 180cm tall.

At the time of the offence he was wearing a blue t-shirt, dark shorts, red underwear, black sunglasses and was carrying a blue and white towel and a green backpack.

Anyone who may have seen the man in the Woonona area on Sunday is urged to contact Wollongong detectives or Crime Stoppers on 1800 333 000.