I transition my students to counting rhythms with numbers in third grade when they begin recorder. I have never found a worksheet that embodied what I wanted so I made my own. This is level 1 which includes 4 quarter note and eighth note rhythms.
Level 2 and Level 3 Rhythm worksheets are now available in 3/4 and 4/4 time signatures.
I have also bundled all three levels here: https://www.teacherspayteachers.com/Product/Counting-Rhythms-with-Numbers-Bundle-Level-1-2-and-3-1970242