I'm afraid I can't give you exact pricing for all of them.

The Tale of Peter Rabbit: from it's 3rd printing in 1902 would run 1/- one shilling.

The Tale of Mrs. Tiggy Winkle: Would also run 1/-

The Railway Children also 1/-

Most fiction and children's books I've seen from that period run 1/- unless you get a special edition that might run 2/6 (half crown) but usually not much more.

Of course when talking about children's literature of the time you can't forget the penny dreadful which ran between a halfpenny and sixpence.

Your best bet is to look on antique book sellers, ebay or other sites. The Net Book Agreement meant that every book should be stamped with the cost on the binding. If you can find an antique copy for sale it usually will have the binding shown and hence will have the price also.