The IGI also has:

CHRISTIAN Robert Alfred s/o Robt CHRISTIAN & BRIDSON chr 08 Jul 1846, Douglas, St Mathews, IOM

XTN, Robt Edwd s/o Robt XTN/ Mary chr 01 Feb 1846, Maughold, IOM

although a later christening of a Robert Edward (1855) to this couple suggests that the earlier one may have died young.

There is also

CHRISTIAN, Robert s/o Ann CHRISTIAN chr 22 Nov 1846, Maughold, IOM
CHRISTAIN, Robert s/o Hugh CHRISTIAN & Ann HOWLAND chr 10 Jun 1849, Andreas, IOM
CHRISTIAN, Robert s/o RobertCHRISTIAN & Ann KILLIP chr 20 Dec 1849, Andreas, IOM
CHRISTIAN, Robert s/o Enos CHRISTIAN & Catharine FARAGHER chr 19 Mar 1848, Kirk Michael, IOM
CHRISTIAN, Robert s/o Thomas CHRISTIAN & Jane chr 22 Feb 1852, Bride, IOM
CHRISTIAN, Robt s/o Wm CHRISTIAN & Ann BOYD chr 14 Nov 1847, German, IOM
CHRISTIAN, Robt s/o Robt CHRISTIAN & Agnes DUNSELL chr 22 Dec 1847, German, IOM

Some of these are in the 1851 Census mentioned by Brian.