I've done lots of 'family barn dances' and in general like to keep the
synced to the music where possible, but a few things can be done.
Some of the musicians I work with are very good at putting in an extra B part when
needed. Since lots of the simple dances end with a long cast off and others
I use the extra B to give them time if the sets are long. That way we can at
each time through the dance at the start of a tune - (if does require some
"wait for the music")
If a dance ends with a cast off and there is not quite enough time to finish,
dances starts with LLFB say, I sometimes tell the dancers to just 'catch up' -
at a barn
dance this often makes it more fun.
I don't like to slow the tempo very much. For dances in long lines, if adults
kids across from them and each line alternates adult child, there are always adults
who can help the little ones get thru in time.
Some simple dances the kids like have an indeterminate finish where is there a pause
between each time thru the dance. See Silly Threesomes
I hope these comments are useful.