Hello, We are planning a trip at the beginning of Aug with a 7 and 9 year old and we're planning on staying at the Beach Retreat. -Is it typically busy during that time - is FastTrack Pass worth it? -Is 2 days enough time to do both theme and water

In August, fast track probably worth it for you only going there for 2 days. The park opens from 10-5, if there are long line on every ride, you won't be able to try everything with your children. We were just there yesterday, on a slow day, we barely able to try everything on 1 park, the water park was closed yesterday due to weather.

Everything in Orlando is crowded in August. I can't speak to FastTrack but Legoland is really pretty small. One or two days would probably be fine.