My contracts do not have an 'end date' either - if I do not make changes to the current one it remains in effective until 'termination notice is given' however they do have a clause that contracts and policies are reviewed annually and any changes will be accompanied with 60 days written notice ...at that time they either accept and sign a new contract reflective of those changes or they give notice to terminate the contract and seek service elsewhere.

I also agree that just because you did not put that 'clause' wording in there does not mean you are not free to change your fees or service or policies with current clients - you would just draw up new contracts and send out a letter explaining that due to XYZ you are having to ask parents to renew contracts with the new fee ... if they choose NOT to accept those new conditions they are free to seek service elsewhere.

Personally I have never had a client balk at a fee increase - they value the service offered and recognize that quality childcare is an investment in their child's future and their peace of mind while at work!