Re: Student Sax
There is no 'student size' for saxophone. You'll either run into the Eb alto saxophone, or a Bb Tenor Saxophone (there are a couple more, however, that a saxophonist would run into later). Students can start on either instrument (both utilize the same fingerings and techique, so switching back and forth is simple)
Beginning on the Alto or Tenor will be a matter of preference for your kid. It may be usefull to speak with his/her prospective instructor about this choice.
Monique and Maxam both have very poor reputations for quality. A number of people make the assumption that such instruments would be appropriate for a couple years for a begginner, but that's mistaken thinking. Such instruments are riddled with problems and resist efforts for readjustment and repair. Such isntruments may not play in tune no matter what you try, and may sound horrible. That is not a good situation to have to learn under and it's almost gauranteed to kill youthfull enthusiasm.
If you must go cheap, go used. Selmer Bundy's, while not great, are servicable and recognized by repair personel and educators and can be had for @$400 in used, playable condition. The better student line instruments are made by Yamaha, but are pricier. Conn and King also make some reputable student horns.
There is so many ways to purchase a saxophone wrongly, and rightly. You may need reputable local advice