The Talmud at Tractate Pesachim 108b-109a relates that
we distribute to them [children] parched ears of corn and nuts on the eve of Passover, so that they should not fall asleep, and ask [the ‘questions’]. It was related of R. Akiba that he used to distribute parched ears and nuts to children on the eve of Passover, so that they might not fall asleep but ask [the ‘questions’]. It was taught, R. Eliezer said: The mazzoth are eaten hastily on the night of Passover, on account of the children, so that they should not fall asleep. It was taught: it was related of R. Akiba [that] never did he say in the Beth Hamidrash, ‘It is time to rise [cease study]’, except on the eve of Passover and the eve of the Day of Atonement. On the eve of Passover, because of the children, so that they might not fall asleep.
The shi’ur of Rav Arele Harel last night noted this instruction, emphasizing that the commandment to “relate to your son” (Exodus 13:8) is an integral element of the Seder night. If you cannot keep your children up, there’s a failure and not everyone can get his children to take a nap.
The main reason why the Seder is relatively late is that the evening service usually begins at nightfall, there is a long davening including, here in Eretz-Yisrael, the Hallel, and add on to that getting home and the last-minute preparations and we end up with the beginning of the seder, this year for example, at close to 9 PM.
Can anything be done? Rav Arele says something should be done.
Just like during the summer months, so, too, should the davening for the Chag be started earlier. The main objection would be the instruction to say the Hallel as it belongs to the Chag. Rav Arele, after consulting with Rav Yaakov Ariel of Ramat Gan and Rav Elchanan Bin-Nun of Shiloh, asserts that since the Hallel is also said during the Seder service, the problem of thinking that the Hallel must be said after nightfall is solved. There is one Hallel for the prayer service (and that service can start before nightfall) and another for the Chag itself which is at the table.
And so, this evening at Shiloh, there will be a minyan (two, actually. one up the hill, the other in the middle) which will begin at 6 PM (mincha will be recited at 1:30, as we all do here). Then they will go home after finishing just after 7 PM and at 7:25 or so, the Seder begins and right after Kiddush, the Shema is repeated as that prayer need be recited after nightfall.
And the children should be able to enjoy the evening without falling asleep too early.
From Rav Arele:
בהמשך לשאלת רבים בעקבות דבריי אמש בבית הכנסת נעם יונתן, הרי כמה הבהרות: