But if there are no errors, it will never echo. Sometimes if data is missing, it is not a sql error. So Blue gave you the line to enter to echo the query above.
$sql="INSERT INTO register (id, YourFirstName, YourLastName, YourPhoneNumber, YourEmailAddress, BabysFirstName, BabysMiddleName,BabysLastName, BabysBirthdate, BabysAge, BabysHeight, BabysWeight, BabysEyeColor, BabysHairColor, BabysEthnicity) values ( 'NULL','$yourfirstname','$yourlastname', '$yourphonenumber', '$youremailaddress', '$babysfirstname', '$babysmiddlename', '$babyslastname','$babysbirthdate', '$babysage', '$babysheight', '$babysweight', '$babyseyecolor', '$babyshaircolor', '$babysethnicity')";
echo "sql: $sql";