While I understand your complaint in general, I think you should probably find that the games aren't terribly disrupted, albeit more due to luck than anything else. The Celtics should be near full strength for the Knicks game, as should the Knicks (they're more likely to be down guys due to injury than Covid). Likewise they should be good for New Orleans and Orlando. As for their opponents in those two later games, the Pelicans seem to be starting to hit their Covid spike, which should also make them mostly clear of this by January, and the Magic have also had at least half their roster infected in the past few weeks, so I'd expect the same for them. The latter two games are near the trade deadline, so someone might be held out for those reasons, but your kids should get to see full Celtics teams against reasonably full opponents, barring the usual injuries.
It sucks for the people who had tickets to games in December (although honestly, I think the real issue with playing the games was that we shouldn't have been encouraging 10-20k people into arenas this past month), but because this spiked so rapidly, the other side of the spike should be pretty smooth sailing for the rest of the season, with an occasional guy out here and there, but not the utter decimation of teams.
I'd also note that, at least in case of the Celtics, the emergency players have barely seen the court. The Celtics have signed 5 such players, only 3 of them have played, and none for more than 2 minutes (and it was a fun story for a night when Joe Johnson got his two minutes). I've seen a bit more Juancho Hernandez than I'd have liked to in December, but he's not a replacement player (this year).