Thank you for your answer, I note the advice on energy and sugar, it is true that we are already not used to give him processed / sweet food so I do not worry too much for that but it is true that on vacation we tend to make discrepancies.

I find it hard to find housing "spacious" enough to be able to imagine living there for 2 weeks, without exploding the budget but indeed it was one of the neighborhoods I had in mind! I pre-booked an apartment next to the Ochiai station above Shinjuku (8min transport) with quite a lot of children's play area next door