sis glysolid_clarins: mas pricey ang enopi (eye level na yata sya ngayon) if I'm not mistaken. Oo naman dapat ipa-enjoy sa mga bata ang childhood nila, and dapat din help natin silang maximize ang potentials nila at a young age.
My kid is in prep, and she's been on the Kumon program since May 2015. They advise parents to stick with the program for at least two years to maximize the benefits Kumon offers. More on building habits kasi sya through constant and consistent practice, so it really does take time. Hindi sya quick fix ika nga. But yes, since monthly mo nirerenew, you can stop/rest any time.
My kid is in prep, and she does her Kumon (math) worksheets on a daily basis. There are times we miss out on one/forget, lalo na pag weekend. Hehe. So she just works on the missed one the next day. Hindi ko alam with other kids, but with mine, she views it as her responsibility. So she knows she has to finish one a day, and has to work on two if she didn't work on one the day before. I don't even have to remind her, nagkukusa sya.
Is Kumon too much for a prep student? Personally ha, I think it's more of how YOU as the parent balances things for her. Give her enough time to play, supplement her learning with fun things to do, if your kid misses out or makes mistakes on the worksheets, don't sweat it - but make sure the child knows na dapat matuto sa mistakes and move forward, keep on improving.

With my daughter, she takes about 10-15 minutes at most to answer a worksheet. The rest of the time pag wala naman sya assignment or school quiz the next day, I let her play, watch a bit of TV if she wants to, maglaro kami together, make stuff together, or we go out and have milk tea or mag-mall to play - even on a school day. Hehe.
She hasn't shown me any signs na ayaw na nya even after 7 months of doing Kumon. To 'test', I tell her, anak hindi ka muna magKumon next month ha. Ay, nalungkot ang bata. Bakit daw, she wants to go back to Kumon pa din daw. She will miss her teacher there and her worksheets, saka malapit na daw sya sa goal nya na letter (they track progress by letters of the alphabet). So there, that's my cue, she's motivated, and she wants to continue.
Pag sinabi nyang ayaw na nya, then that's when we'll stop.

I think same concept works naman with other enrichment classes we enroll our kids to - we take our cue from them - kung gusto ba nila talaga, is it helping them, at kung gusto pa nila ipagpatuloy. With enrichment classes naman, there's no harm in trying naman eh (there is gastos though. hehe), but there is pag pinilit lang sila.