Child domain prompting for Username & Password

I have main domain abc.com and the child domain
child.abc.com both under same forest. Each domain is in
its own subnet and connected by a multihomed router. When
I try to browse resources in child.abc.com which have full
permission for all the domain users of abc.com it prompts
for Username and Password, but when browsing resources in
abc.com from child domain everything works fine. I can
ping, trace, nslookp, dns and wins everything is working
fine. Someone please help where I went wrong, the issue is
critial for me and its getting frustrated trying to figure
out the problem.

Thanks
Sura