I concur... the E+ fee to the midwest is like $45 each way?
Keep in mind, 2 of them are kids and really, the extra legroom doesn't matter much to them.
If you need them to sit together and don't want to pay the fee, have them sit in E-. Its not like UA is making the littlest one sit alone.
I have 3 kids and sometimes UA made an exception and got us all into E+ and sometimes not. I never expected it.
What I did do though, was when they had Elite Choice I would nominate one of my kids as Premier Associate and then we could get everyone into E+.

Also beware, even if they put you all in E+, sometimes the automated sweeps will sweep them back to E- unexpectedly and you get a nasty surprise later when you find not only is everyone in E- but maybe not even sitting together!

The new E+ companion rules for 1K should be a big benefit to the OP when he is travelling with them, so should be thankful for that. The wife doesn't have to score Premier anymore to get everyone into E+.