A. It is certainly understandable that families with young children would want to have an earlier start to their Passover Seder, especially when nightfall is 8 or 8:30pm these days. An earlier Seder before nightfall may have many benefits but it doesn’t fulfill the Halachic obligation, since the Mitzvot of the night must be done after dark.
So, what is one to do? Best case scenario is to try to both honor and respect your families (which is also a Mitzvah, of course!) and do the Seder essentials yourselves after nightfall.
Practically speaking this may mean doing your Seder a little out of order (ironic, because the word Seder means order). The four cups of wine, Matzah and Maror, and at least some retelling of the Exodus must be done after dark. But you can participate in your families’ earlier start, say much of the Haggadah along with them, asking the questions, dipping the vegetable, singing dayenu, and spilling out the blood for the plagues, even eating the meal (or parts of it) earlier with them, and then doing the Seder essentials once nighttime hits. Think of it as a warm up for your own Seder (or essentials thereof) that will follow after dark.
This arrangement may not be ideal, but you are not the only one dealing with this. Some respected synagogues and Chabad Houses follow a similar pattern to allow families with young children an earlier start time so that they are comfortable to participate and still do the essential Seder Mitzvot after nightfall.