Gloria, you haven't given us a lot to hang our collective hat on in order to give you the correct answer. 1) Is your son EU citizen? 2) Is he on a tourist visa to the UK? If not, which visa is he on? 3) Are you asking about your son making a visit to France under the Schengen waiver program? 4) If so, has he had any previous visits to the Schengen area in the past 180 days? 5) The "3 weeks" - is that exactly 21 days including arrival day and departure day? 6) How long between the "3 weeks" and the "family" trip? IF the answers are something like 1=no, 2=yes, 3=yes, 4=no then by taking into account 5 and 6 you can now say if on each day during either visit has he been within the Schengen area for more than 90 days in the previous 180? If the answer is that no he has not, on very single day, then yes. If he has, on even one of the days been in the Schengen area 90 or more days in the past 180 - then no, he would be breaking the law. If the conditions in 1-4 are different then the rules are or may be different.