Imagination Station-Problems in Plymouth #6 by Marianne Hering and Marshal Younger illustrated by David Hohn*

Cousins Patrick and Beth travel back in time to Plymouth in 1621.
"The Christian Magic Tree House"
My second grader brought this home from his school library.  He read it to himself.
His favorite part was the capture of Hugh, a villain from another time period who is causing havoc wherever he goes.
*Highly recommend the series.