Urgent need for apartment for 3 month contract!

Hi my name is Venla and I come from Finland but currently I am staying in Thailand for my bachelor studies. I am coming for exchange period to Berlin School of Economics And Law (Lichtenberg campus) from August to November 2016. I'll be arriving to Berlin on 2nd of August 2016 and I am in dire need of an apartment since my arrival is getting closer and closer. Apartment should be suitable for three persons since I am coming with my 2 year old son and my mother. Desired location would be not more than 30 minutes away (maximum 40 min) from my university area. Apartment should be near by walking distance of public transportation and it should hold at least two different sleeping places (Bed or sofa bed)

WE NEED ONLY APARTMENT FROM AUGUST UNTIL NOVEMBER!

Since our time has ran low with the apartment search we will be renting hotel room for first week of our stay in Berlin