The Parenthood Tax Rebate is not capped as mentioned in your article. If I have 4 children, I will get 10k + 20k + 20K = 50k in total.
See:
http://www.mof.gov.sg/taxation/reliefs_rebates_table.html
http://www.iras.gov.sg/irasHome/page03.aspx?id=6054