Dear fyzzio,
Estherderu explained in detail that GMFM 88 can be used as for children with developmental delays other than CP. score sheet of this test is available online and can be print out for use. as your original question was about detailed information on development of walking and balance/ locomotor skills/ "norms" for children under 5, I still believe that score sheet can provide you a guidline in a sequence that how children acquire normal developmental stages regarding development and balance. you can use those one by one to screen and refer your children. yes surely you would need a manual in order to use GMFM as a standardized test. But till you are not in the position to get the manual, atleast this score sheet may help you to get the idea what to check first and what is expected next.

regards,
Humera.