Yes, parents applying together with a minor can apply online
As a minor, the minor must:
- be under 18 years of age on the day you sign the application
- be a permanent resident (landed immigrant) of Canada
- have at least one parent (includes legally adoptive parent) who is a Canadian citizen or who will become a citizen at the same time as you (applying together as a family)
- can’t have any unfulfilled conditions relating to their permanent resident status
- can’t be under a removal order (asked by Canadian officials to leave Canada)
- can’t be inadmissible or prohibited on criminal or security grounds.
EDIT: if you use the screening tool, you can clearly see that minor applying with at least one parent who will become a citizen together at the same time can apply online
https://citapply-citdemande.apps.cic.gc.ca/en/screening