Is this responsible parenting?

So its the end of Christmas vacation from school and today they were supposed to go back but my 4 year old nephew has not went to school but his 16 year old brother has. He's not acting very sick because he's running around and playing and his parents are not suspicious. I don't think it's good parenting to let your kids stay home from school after a long vacation just because they don't want to go back. For reasons I don't want to talk about I live with my sister and nephews. I'm not used to young kids but now have to deal with it until I'm able to go out on my own (trying to make enough money). This might just be me complaining about having to be around him longer and I am aware that I'm a bad aunt, however I still don't think it's good parenting to let your kids stay home after a long vacation because they need to learn.

Is this responsible parenting?
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