regression=# \set VERBOSITY verbose regression=# ALTER TABLE test ALTER COLUMN a TYPE numeric; ERROR: 42P16: constraint must be added to child tables too LOCATION: ATAddCheckConstraint, tablecmds.c:4467
which appears to have been added in commit cd902b331. I think the commit Pavan is looking at just moved the logic around.
I also though that for a moment, but the commit that I mentioned did not move that error message from somewhere else. I also tested by resetting to commit 1f0363001166ef6a43619846e44cfb9dbe7335ed (previous to the offending commit) and don't see any error.
But since you're seeing it, may it was taken out by some other older commit and then added back again. Will look more into it