"Feel the rhythm! Feel the rhyme! Get on up! It's bobsled time! Cool Runnings!"
That quote/scene goes through my head (and almost out my mouth) everytime I encourage a student in a cello lesson to "feel the rhythm." And if the quote does slip out my mouth, it's usually received with a really strange look. There aren't many kiddos with a strong background in 1990's films.
Rhythm is a strange bird.
Some teachers like to present rhythms by doing fractions, which is undoubtedly an important skill to learn. But head knowledge usually does not equal feeling it in your soul. Rhythm is all about flow. So if you and/or your child are working on a tough rhythm and can't quite "get it," don't give up on excellent execution of it, but ease up on the pressure to perform and focus more on the flow of the phrase. Rhythm will come.
Practice Games for Rhythm
"Foot Thumping" This is a classic one that most musicians, including myself resort to when a tricky rhythm pops up. Play the song on your instrument while thumping your foot on each beat. Violinist, violists, and the like can actually walk around the room, stepping on each beat. Cellists are at a disadvantage here, since we're glued to our chairs. [Warning: Conductors detest foot thumpers so don't make this a habit.]
"Rhythm Bouncing" Listen to or sing the song or rhythm while bouncing a ball on each beat. This really helps to subdivide the space/time between each downbeat. Adults shouldn't ignore this one, it can actually be quite tricky! It's great way to incorporate more listening into your practice. Extra Challenge: Try bouncing the ball on the 1st and 3rd beat, and taking a step on beats 2 and 4!
"Blind Rhythm Review" You'll need a partner for this one. Without the cello (or other instruments), clap/tap/snap out various review songs. Try and guess the song without the pitches! This can also be modified for a group lesson: Sit in a circle and pass the rhythm around by tapping it out on the back of the person next to you. Once it comes back around, see if it's still the same rhythm. It's like "Telephone" but with silent rhythms.
"Syllable City" Match up words and phrases to songs or difficult parts of a piece. Be sure the words truly match up with the beat though. Which rhythms would match up to the following phrases? "Apple Pie... Apple Pie..." and "Mola-sses. Mola-sses." and "Lollipop. Lollipop."