A man posed as a health visitor to try and trick his way into two homes in Blackpool, police said.
A warning calling on all parents to be vigilant has now been issued after the two incidents, which happened in Bloomfield Road, central Blackpool, on February 13, and in nearby Ansdell Road on Friday.
Both times the man, described as white, in his 50s, with grey hair, was unsuccessful.
Det Sgt James Edmonds from Blackpool CID, said: "These incidents are concerning and we would like to reassure people that we are doing what we can to try to find this man.
“Thankfully he has not gained access to these properties or to any children on these occasions, however if anyone is concerned that they may have been a victim then we would ask them to contact us.
“We would also like to remind people to please be vigilant when people call at your door unannounced.
"Always check for ID. Genuine callers will always have identification. If you are still uncertain, phone the organisation and confirm the person’s identity.
"Genuine callers will be happy to wait. If you are not expecting a visitor, do not know who is at the door, have any doubt or feel uncomfortable do not open the door.”
Police said the man told a resident in Bloomfield Road he was 'there to do a check-up on a child who lived there', but was not let in the house.
After returning to Ansdell Road, he called at a house but was only able to speak with a neighbour, and 'said he was there to carry out a health check on a child who lived there', the force added.
The neighbour then alerted police, who carried out checks to reveal the man is not a bona fide health worker.
Anyone with information should contact police on 101, quoting log number LC-20170308-0771.