Harry Potter studio tour London

Difficult, no. But you'll be taking the train everywhere, then connecting to the bus or tube. (Look at rome2rio for the various transportation options). How far are you from the train station in Hemel Hempstead? May I ask why you are staying so far out if most of your days will be spent in London?

At the moment (going up in January) an Off-Peak Travelcard from Hemel Hempstead to London is £22.80 per person. Your daughter will pay the same as it is unlikely that she paid £30 for a 16-25 Railcard, so the two of you will pay £45.60 per day just for the transportation (doesn't include any Hemel Hempstead buses if you need one to get to the station - parking at both Hemel Hempstead and Apsley is extremely hard to get and very expensive). If you go for this cheaper Travelcard you should know that it is not valid on trains or Underground before 9:30 M-F, and is also not valid on trains between 4pm and 7pm M-F.

If you don't want those time restrictions you will need an Anytime Travelcard. They are valid anytime but they cost £28.80 pp or £57.60 for the two of you each day, and as emma said above with a degree of understatement trains in the peak are sardine cans.

I worked trains in and out Euston for many years on that exact route. They can be real basket cases. Most of the time they run to time or close but they get really rammed south of Leighton Buzzard or Tring in the morning from about 6:30 until around 10:00 or so. Some trains calling at Hemel Hempstead start all the way north in Birmingham and in the morning peak add large numbers at every stop. Both semi-fast trains originating at Birmingham or Northampton and stopping trains originating either at Milton Keynes or Tring will call at Hemel Hempstead. In either case if you try to travel before 10am you will be boarding trains which have been "standing room only" for several stations before Hemel Hempstead and very few passengers will leave the train before Watford Junction, but they will probably be replaced 2 or 3 to 1 there. From Hemel Hempstead into London the stopping pattern will likely either be Hemel Hempstead, Watford Junction, Harrow and Wealdstone and finally Euston or the slow train calls Hemel Hempstead, Apsley, Kings Langley, Watford Junction, Bushey, Harrow and Wealdstone and finally Euston.

In the afternoon the trains to Hemel Hempstead will be "standing room only" from 3:30pm or 3:45 pm until about 7:30pm or so. Many people trying to save money - regular commuters making the same journey every day all year long - take the two or three closest off-peak trains either side of the peak period, and the those trains are as bad or worse than the nearby peak trains.

This isn't to give you a long boring story to read but to try to prepare you so you can make the best decisions and have the best trip with your daughter. If you understand the true situation you can be prepared.

There are other, different issues on weekends.

How many days will be making this commute?