Personally I’d go to Chester and back, lovely city with a very good zoo, if that floats the kids boat (so to speak). Very roughly;
End day 1 (assume you have 3 to 4 hrs) you should make Middlewich.
End day 2, Barbridge (Chester is a right turn when you get to the Shropshire Union, but I’d initially turn left and moor near the pub. You can turn round about a mile further down.
End day 3, Either moor at the Cheshire Cat pub on edge of Chester (or go all the way into Chester)
End day 4, stay in Chester (maybe start journey back)
Then up to you how much you push to get back
Just my views having done the trip a few times.
as for bikes, towpath may be muddy in a few places but generally good for cycling. May be worth checking with hire base regarding bikes on roof or in front well deck (good locks advised).