Mr Johnson spoke to MPs after sunshine on the English Channel and there was an upsurge among migrants arriving in the UK on Tuesday and Wednesday due to the calm sea.
More than 100 people were brought to Dover this morning aboard a Border Force patrol ship and a lifeboat.
Several children and toddlers are being cared for spot
Addressing the House of Commons, Mr Johnson said: “I have a lot of sympathy for those who are trying to keep their kids in dinghies or even kids in paddling pools and trying to cross the channel.
“But I have to say that what they are doing is falling victim to criminal gangs and they are breaking the law. They are also undermining the legitimate demands of others seeking asylum in this country.
“That’s why we’ll take advantage of leaving the EU by changing the Dublin rules on the return, and we’ll deal with the rigidity of our laws that make this country, I’m afraid, a target for those who will exploit the weak and a magnet in this way.”
As it stands, the Dublin Regulation means that asylum claims must first be processed in an EU country where anyone claiming to be a refugee will receive a position.
If an immigrant seeks asylum in the UK, the authorities can check if the person’s name has already been registered by the authorities elsewhere in the EU. If the claimant is logged in, for example, France, Britain can then begin the process of returning to France the person whose asylum application is expected to be considered.
The Home Office was forced to abandon a flight last Thursday for the repatriation of illegal Channel immigrants to Spain after human rights lawyers took last-minute legal action.