While a number of people have blamed online sales for the demise of Toy R Us it could not be further from the truth.
The parent company in the US went into Chapter 11 bankruptcy last year and you can be sure they were still draining the UK operation. Having said that, in the UK the company failed primarily because they could not pay their VAT bill. Money they had already collected from customers.
From the comments here and elsewhere, it is quite clear that the stores were dated, staff not customer focused, lack of a quality online presence and very expensive. Most products you have been able to purchase elsewhere, considerably cheaper and that is without going online. John Lewis sell Lego around 25% cheaper, Smyths Toy Stores along with The Entertainer are doing a roaring trade.
Maplin are a different kettle of fish. Not sure what management tactics have caused them to fail but I remember the original Maplin from the early 1970's who primarily were mail order, dealing with electronic geeks. They at the time only had a couple of stores. There failure to my mind has been trying to be an electronic toy store, but at a price that Joe Public was unwilling to pay. Remember Tandy? The way they grew and fell should have been a warning for this type of store.