Parents who fail to register and get a birth certificate for his or her child will be forced to pay for services that are normally given to citizens of a state, and possibly be sued for some level of abuse or negligence for failing to give their children the rights of a citizen.
The biggest consequence for the parents would be expense. If a child does not legally exist, then he or she will have no rights under the law and as a consequence, will be deprived of many privileges given by the state. For the parents, this means they will have to pay for things that would normally be freely given by the state. This includes health benefits and free education. The parents will also not be eligible for other welfare benefits given to parents. For example, how can a parent get a parental leave if there is no proof that a birth took place?
Furthermore, given some creativity, the child may also sue his or her parents for failing to provide him or her with a birth certificate. There are countries, for example, where the failure to register a child's birth is considered a violation of the Constitution.
However, the biggest consequences of not getting a child's birth certificate is not really on the parents, but on the child himself.
Legally speaking, a child who does not have a birth certificate does not exist. So, aside from not being eligible to receive state benefits, the child may also be vulnerable to abuse and exploitation. Without a birth certificate, the child will have no proof of his or her real age. Thus, the child will not be able to receive the protections that governments normally given to children. For example, without proof that they are minors, a child can be forced to marry, be tried as an adult in the justice system, and be forced to work in harsh environments that are not suited for children. Normally, governments can step in and prevent this from happening, but without a birth certificate, there is no way for governments to justify an intervention on the basis of protecting the child.
Finally, without a birth certificate, the child will have a hard time moving in society. Odds are, the child will not be able to get a passport and travel, the ability open a bank account, and gain legal employment. After all, these things require an ID, and you won't get one unless you have a birth certificate.
In Africa there are no consequences cos I happen to be among those with no birth certificate cos I was born in the interior part of a village where there are no hospitals or health centres. As it stand, I use Court Affidavit of Age Declaration.
Here in the Philippines, there's nothing I can think of nor I've heard of any punishment for parents not getting birth certificate for their children.
But the consequence about this would be felt and pay for by the child itself. It will start with being baptist for a religion especially Christianity as birth certificate is one of the requirements.
Then there's school which means they won't be able to have access to education. When they grow up, they wouldn't be able to find a proper job because important papers and ID need birth certificate such as the social security system.
And no proper jobs means you're not paying taxes because you have no record of your existence and of course you won't be able to have benefits too like discounted health services.