Crafts or science experiments for grandchildren

What about a bug collecting kit? Something like this? www.hobbycraft.co.uk/kids-first-wildlife-detective-kit/646375-1000?glCountry=GB&gclid=Cj0KCQjw7ZL6BRCmARIsAH6XFDIzKqHX74BzcIWEQfz6qpJUgYn6WsONoWy4ZtnJ6Vx2WWtjVDGjp_8aAizmEALw_wcB&gclsrc=aw.ds

It says for Five years and upwards, but my kids were well up to this stuff by four.

We collected autumn leaves and made autumn pictures with leaves, pasta and glue.

Growing things such as mustard and cress, beans in a jam jar etc is interesting.
Cooking eg baking helps with maths and science; it's amazing how all the separate ingredients, when mixed together, and heated, can produce a cake.
Science is interesting when there is an end result which can be eaten.

I found some hand puppet kits which needed sewing but a young child can manage that because the holes are pre-punched. She could put on a puppet show afterwards.

My DC had a book called How Science Works by Judith Hann but it was for perhaps Y3 and above.

I found an easel in the charity shop and the Early Learning Centre had lots of paints, brushes, sponges, coveralls etc suitable for younger children. They liked to paint standing up (if the weather's good in the garde, saves mess).

If you want to develop scientific understanding in a four year old you can't do better than unlimited access to to water, sand and dough with a whole variety of everyday implements (for want of a better word). Raid the kitchen cupboards and the shed.

As far as craft goes, masses of bits and pieces to cut, tear and stick. Loads of paint. Different brushes, sticks. Different papers.

A minimum of adult intervention. Four year olds have plenty of ideas of their own if they're not constrained by what the adult thinks is good, ?

My granddaughter is four and would find it impossible to follow a book or magazine without considerable input from an adult, but if you search online for 'Craft books for four year olds' there are a few you might like. But the grown-ups will still need to help! All the best for your search.