Filing taxes online vs a professional in person

I’ve always filed mine with a professional and it’s free , last year I only had my daughter to claim and got back alil under 3,000 .. I just went to turbo tax and put all my info in and their talking about $700 .. 🤨 but this year I have my son and daughter to claim . Idk how it went from the thousands to hundreds . And might I add I only worked for 2 months before this w2 came . And last year I only worked for 7 months . I’m not sure if that makes a difference . And also I heard different websites tell you different amounts of money you’ll get back . For example turbo will da your getting back 300 but freetaxusa will tell you your getting back 3,500 .. why is that? Sorry if I sound dumb or anything I’m 19 and don’t know anything about taxes . It’s alil confusing to me