That’s certainly a popular child’s version of history, but children have an excuse for being ignorant. Adults not so much. Slavery in the US preceded the Democratic party by 200 years and when the party was founded in 1828 slavery wasn’t part of the national debate. Tariffs, internal improvements, and the national bank were the issues day, the same ones that dominated the 1824 election. One of the two Founders of the Democratic party, Martin Van Buren, was opposed to slavery, was opposed to the admission of Texas as a slave state, and was an outspoken abolitionist. Apparently he didn’t get the memo informing him that the party he co-founded was “the slave party”. Go figure. Maybe that’s what happens when google isn’t your primary source.
When Van Buren was in power, he made his peace with the slaveowners and didn't act on whatever dislike he may have had for slavery. He supported the gag rule that forbade Congressional debate on slavery because he thought it would keep the country (and the party) from falling apart.
Van Buren was not an abolitionist, though he wasn't a fervent supporter of slavery either. After his White House years he grew disillusioned with slavery, arguing that the Founders had wanted slavery to be abolished eventually.
That was an uncommon position for a Democrat to take in his day, but one that did have some support in the country and wasn't considered abolitionist in the sense that Garrison, Douglass and others were.
Van Buren ran on the Free Soil ticket in order to keep slavery out of the territories, not to free the slaves. His nomination had a lot to do with the fact that his son was one of the party leaders. Van Buren temporarily left the Democratic Party to run on the Free Soil ticket. Afterwards he was back to supporting Pierce, Buchanan and Douglas and discouraging debates about slavery.