I wouldn’t loose sleep over this. I had same situation last year, we had originally booked for 4 for all our ADRs, than a 5th decided to join us 2months prior. We had all the tough ADRs, (BOG, CRT, Ohana etc.).
By a few weeks prior to our trip we were able to get everything updated for 5 people. Used Touring Plan Rez finder and a bit of refreshing here and there. We were even able to keep same ADR times (give or take 10-15mins for a few)
Thank god everything worked out, We were prepared to sneak our 1yr old. Also, we found WDW to be flexible: we showed up 30mins late, NP, showed up 30mins early, NP, seated early. I can’t see how they would nit pick on a toddler who wouldn’t actual take a real chair and would be in a highchair sharing the same table type.
For people talking about “capacity”. I had NEVER seen anyone with a clicker at the door counting who is going in and out of the restaurant. And we traveled during Thanksgiving week. Lots of rotating tables empty.