I did not have enough points for a couple's file during the immigration process to have the CSQ, which is why I removed my wife from the file.
Not clear to me what advantage there was to leaving the kid on that app, but that's your business, I presume it made sense at the time.
On the other hand, a request for a visitor visa for my wife for the purpose of accompanying my child in order to validate his PR visa, do you think he accepts it?
No harm in applying for the TRV really.
Two issues with this: first, it's just plain likely to take too long - while I don't mean kid needs to depart literally tomorrow, questions may come up fairly early in the process (not clear when you submitted), and you'd be better served to avoid that. I.e. what if it takes four months to get your spouse's TRV?
Second, not clear your spouse would get one and could get refused. Depends on other factors but 'accompany my only child to become PR' is going to read - likely - as "I plan to stay forever too."
And last: you haven't mentioend but when your child's PR visa expires and when you submitted is a big factor too - if your kid's visa expires in three months and you only just applied, close to zero chance your spouse will be approved and get visa in time.