Other mistake: Near the end of the film when Jack-Jack is manifesting various abilities, his first display is of the human-torch-type of superpower. This would have burned away all of his clothing, yet (for obvious reasons) his diaper remains intact. This is particularly apparent as designer Edna Mode's costume for Jack-Jack was earlier shown as fire-resistant, but he was not dressed in his outfit during this scene. (01:44:15)
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Suggested correction: This is definitely intentional, not an error. We see Jack-Jack use his fire powers without burning his diaper in Incredibles 2. Having fire powers without burning clothes is just a retcon.