If the father follows the Rabbenu Taam’s shkiah, then the children must follow it as it has to do with an issur and not a chumra. At least kitniyos was assered by rishonim as mentioned by the Mordechai 588, and the RMA O’CH 553,1, whereas gebrochts, to my knowledge, became a custom in the 18th century as mentioned in the Sharei Teshuva O’CH 460 s’k 10. They say that potatoes were not included in kitniyos as the geonim did not have any. When the Chayei Adam wanted to asser potatoes, they said you are taking away the Chayei Adam.
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