317 forever - you can't do links like that as they rely on session cookies to work. Also the OP said 1 adult and 1 child. Nevermind, better luck next time
Joshypie - The through fare is as follows:
Dewsbury - Warrington Stns
CDR - OFF-PEAK DAY R TPE
00000 - ANY PERMITTED
1 Adult @£ 11.60 = £ 11.60
1 Child @£ 3.35 = £ 3.35
__________
£ 14.95
Standard Class Return
That seems fairly reasonable to me. It's more than the cost of splitting at places like Manchester, Stalybridge, etc.
It may be possible to reduce the price, but it seems unlikely.
It's one of the rare examples where you are NOT punished for travelling further!