Hello,
as you say, it is difficult because there doesn't seem to be another candidate.
Free BMD has births:
September 1875
Charles William Poskitt Pontefract vol 9c page 127
December 1875
Charles Poskitt Tadcaster vol 9c page 778
1881 has your Charles W living in Tadcaster district (to complicate matters)
The one born in Tadcaster district is possibly this chap:
Charley Poskitt 5 yrs born Allerton Bywater living with mother and stepfather George and Jane Ellis. They are in Dewsbury area in 1881.
1871 has Jane's husband as Thomas Poskitt.
William was a collier and it may have been that the name Charles was written for the father's name by mistake.They are also living in Castleford by 1891.

regards
heywood