As it was ask before a lot of times....here is a good overwiev how many children/daughters and stillbirthes Nikolai and Alexandra had.
Aleksandr II Nikolaievich Romanov, Tsar of Russia b. 29 Apr 1818, d. 13 Mar 1881
Mariya Nikolaievna Romanov, Grand Duchess of Russia b. c 18 Aug 1819, d. c 21 Feb 1876
unnamed daughter b. 22 Jul 1820, d. 22 Jul 1820
Olga Nikolaievna Romanov, Grand Duchess of Russia b. 11 Sep 1822, d. 30 Oct 1892
unnamed daughter b. 23 Oct 1823, d. 23 Oct 1823
Aleksandra Nikolaievna Romanov, Grand Duchess of Russia b. 24 Jun 1825, d. 10 Aug 1844
Elizabeta Nikolaievna Romanov, Grand Duchess of Russia b. 7 Jun 1826, died young
Konstantin Nikolaievich Romanov, Grand Duke of Russia b. 21 Sep 1827, d. 29 Jan 1892
unnamed daughter b. 5 Oct 1829, d. 5 Oct 1829
Nikolai Nikolaievich Romanov, Grand Duke of Russia b. 8 Aug 1831, d. 25 Apr 1891
Mikhail Nikolaievich Romanov, Grand Duke of Russia b. 25 Oct 1832, d. 18 Dec 1909
Have a look to the source:
http://thepeerage.com/p10069.htm#i100689Hope, I could help:-)