How old are they, MamaBear? My youngest was 8, I think, when I bought some handwriting practice books from WHSmith and made him practise cursive writing at home every night, starting from practising individual letters and letter joints, as they should have done in reception - only 10-15 minutes a day, but consistently, and it helped.
DS1 recently started writing smaller and smaller (when I asked him why, he said his books looked much neater this way
), to the point I found it hard to read. He wouldn't listen to me, so I had a quiet word with his English teacher and she wrote a few comments in his book along the lines of 'bigger writing, please' and ' you will lose marks in public exams if the examiner can't read your essay'. Fingers crossed, it's working so far!