In general if your child is above 4 they should be applying for a study permit to live in Canada and attend school. Although some policies state that TRV is acceptable and it will still work for those under 4, if your child wants to live in Canada then they are not truly a visitor which and need a permit that allows them to live in Canada. For example a spouse accompanying someone on a work permit should be applying for an SOWP even if they don’t plan on working because the permit allows them to live in Canada not just visit.