it depends on how long ago it was,but im pretty sure that when you apply for any job with kids,you willl have to have a crb check,which will show up your conviction,so you better disclose it when appling for the job,whether it will hinder your chances of the job,i dont know
Any convictions that occurred after you legally became an adult will stay on your record forever. The time limit you're thinking of is how long before they are classed as 'spent' ie you don't generally have to disclose them to anyone. Convictions generally are spent after 7 years but it does depend on the nature of the offence. More serious offences such as sexual offences and murder are never 'spent'. The law now gives certain circumstances when 'spent' convictions must be disclosed, this includes working with children and the vulnerable, even as a volunteer. As Steve says, you will have to disclose your conviction if you wish to work with children and your prospective employer will take into consideration how long ago the conviction was and the sentence imposed by the court before making a decision as to whether to allow you to volunteer. Please don't let your conviction put you off applying though, as many people have convictions and still get accepted as volunteers! Hope this helps and good luck!