beijing - xian with child 4 yo

Hi need to consult my itenerary if its already efficient for family with kids with 4 years old
Day 1: arrive from KL 1 am stay at novotel xin qiao. Go to
Olympics building, t square, forbidden city, qianmen street
Day 2: great wall, acrobatic show, wan fu jing street
Day 3: the temple of heaven take sleeper train to xian
Day 4: arrive in xian at 8 am directly go to terracota warriors, bell tower, moslem quarter, then city wall. Catch bullet train back to beijing
Day 5: beijing zoo, summer palace with ferry yhen hu tong walk tour
Day 6: fly back to KL 2 am
Questions: is it my itenerary already efficient to take kid 4 year old?
Could you suggest where to eat?
Where and when should I buy train tickets?
Traveling in town is it more easy to take subway or buss?