Brazil is quite a big country, so it depends how much travelling around you want to do. Most international tourists go to Rio, Bahia and Iguacu, so outside of these places you will find it is mostly Brazilian tourists, but note that those three places are all a long way from each other.
It really depends what sort of thing you like, but the Pantanal might be good with kids. Hard to get to though.
It may be worth just picking a region and exploring it.
The whole of the coast has beaches, so they are easily found although it depends on the time of year. The south isn't warm in the winter.
Be aware of the crime levels, so you take precautions, but don't let it put you off.
Also, and not really relevant to this, but plenty of lone women travel around South America without any problems.