I don't want to be flippant, but realistically if you're advertising that you're going to be lenient and waive the law for young people in the country a certain period of time, you're bound to get all kinds of new children finding their way into the country and presented by existing residents as children who've been in the country for a long time.
Now, if you advertised that there's a shoot to kill order for anyone discovered trying to cross the border illegally at other than regulated border crossings, you'd likely have fewer taking the risk. Alternately, if you advertised that anyone discovered crossing the border illegally would be sent to internment camps for a minimum of 5 years and then deported, you'd likely have fewer taking the risk.
It's only human nature. If you tell a child that they can't have icecream but if they can find a way to break into the icecream parlour you'll give them a banana split, with no penalty if they fail, you're going to have lots of kids trying to find a way to break in.