I have a lovely book about pollination that may be too old for your group but in case it helps someone else…
The Clover & the Bee by Anne Ophelia Dowden
Water cycle – there is a Magic School Bus episode that does a great job explaining it in a fun way. (Shocked I would recommend a video! But my boys loved this one.)
Gladys Conklin and Robert McClung both have wonderful books on ladybugs.
Lucky Ladybugs – Conklin
Ladybug – McClung
Not solely about sundials but talks about them in conjunction with telling time…
How Do You Know What Time it Is? By Robert Wells
Clocks Tell the Time by Alma Kehoe Reck