My DD changed schools just after one term in prep, was a big transtion as I'd left my ex, so we had that to deal with plus new house, new school. But she adjusted really well, better than I expected, I spent alot time stressing and worrying, now near end term 3 you wouldn't even know she started later than everyone else.
But thats just our situation, I know it can be different from person to person. You need weigh up what best to do for you. Whats better or worse, being without your DH/ their dad for so long or having your DS start school later?