To receive the enhanced UCCB, families may have to sign up. If you have children under 18 for whom you have not previously applied for the UCCB or the Canada Child Tax Benefit (CCTB), you will need to apply for the enhanced UCCB. If signing up after May 15, 2015, the payments will start later than the July 2015 payment, but will still be retroactive to January 1, 2015. You can expect to hear from Canada Revenue Agency (CRA) within 80 calendar days after they receive your application.
More information is available from the CRA at this link