It really annoys me how some parents insist on correcting their child when they say things like "I ranned". I have a degree in linguistics and child language acquisition, but don't believe anyone needs a degree to realise that this grammar is a natural journey, and what your child's actually done is be very intelligent, because they've recognised that to form a past tense (in the regular sense) you can add -ed on the end of some words.
Does it irritate anyone else to see parents prodding their kids and saying "NO! Its "I ran" ?