Can you donate your credits to other members?
No. You cannot share credits between accounts.
Credits are not transferable directly but premium members can give out some of their own credits as a special bonus for their critters. You'll see a menu item on crits you've received giving you the option to "Give extra credit".
The basic idea is that those with a lot of credits can give those less fortunate a little something extra for great crits. Please note you can only donate 1 extra credit from your account per crit.