I would say that either of those two choices, Clifden or Achill, will be quite the push both from Corofin and back to Dublin. I would suggest adding a night to both Dingle and Corofin and then heading to Dublin from Corofin.  You could do a Connemara day trip from Corofin.

Achill with a toddler in tow would not be my choice. There are more choices for rainy day activities in and around Dingle and Corofin.

I chose Cahir because we're staying at the Carrigeen Castle B&B and want to see the Rock and Mitchelstown caves too. I found a nice self catering house near Corofin & Burren national park. I know its a little out of the way but it gives my kids lots of space to roam and we should be able to do some nice walks from the house. And it looks like its within close enough driving distance to Lahinch for golf for the boys, Drumoland for tea for the girls, and the cliffs (also might go to Aillwee caves if we don't get to see Mitchelstown caves). I'm thinking of spending a third night there to give us some downtime and then spending 1 night at a B&B near Clifden and spending the day exploring near there. I'm trying to fit in a lot of sights but leave things flexible since with 2 little ones I never know how much we'll really get to see in one day. :) I'ld love any advice on sights I'm leaving out too. Thanks!