We have a business trip in Munich in February. We have 3 days to travel from Munich to various areas. Our group includes a 4 year old child. We were thinking Neuschwanstein Castle, Therme Erding (thermal spa) and Salzburg. Is that doable? Is it better to have day trips from Munich with a car or train? Thanks for your help

Yes doable.

Definitely train (and/or bus in the case of Neuschwanstein). There are also organized tours to Neuschwanstein. I've done it both ways several times and prefer the do-it-myself route, but depends on you. Do book well in advance for the castle.

Having said that, I am not familiar with the Therme Erding and don't know how far it is from the closest train station, so do take a look at that. DB shows it's just over an hour by train from Munich.

February can be a tough month, weather-wise. It was our least favorite when we lived in Austria.

If you're all into the cold, Zugspitze might be an idea; you can take a cogwheel from G-P to Zugspitzplatt. Salzburg is a couple of hours by train; might not be terribly interesting for a 4-year old, though. Königsee would be beautiful in winter. Rothenburg ob der Tauber is charming, though it would be a long day trip

I would check the policies at the Therme regarding children.

Konigsee is indeed beautiful in winter. Here's a photo of it from a winter trip in 2016. Hoping to get there in summer this year.

Neuschwanstein may be a disappointment. Due to larger crowds, they have really shortened the guided tour. Everyone in your group gets a headset and audio guide in your preferred language and the group is herded from room to room.

We loved salzburg and it's a short(ish) train ride from munich. Castle, carriage ride, children's museum.