We generally rely on prayer schedules out of necessity in the states as opposed to the blessing of hearing the muadhdahaan call the athaan when we were in the Muslim lands. But it is beneficial to have the kids learn how to naturally tell when the salaat comes in. In the past, we have learned how to tell the approximate time of day using the sun by going outside at various times of the day and recording where our shadows were. I'm looking forward to trying to do something similar with the information we've come across below, in shaa Allah.
Below is an excerpt from a post found at SalafiTalk.net which describes the times of entrance and departure of each of the 5 daily prayers.
The Legislated Times for the Five Daily Prayers
The Muslims have never differed over the fact that the five daily prayers have specific times that have been legislated in the Sharee'ah.(2) Allaah, the Almighty, has said, "Verily, prayers have been prescribed upon the believers at set times."
The following is a listing of the times of the five daily prayers, with a brief reference to their relative proofs from the Book and the Sunnah:(3)
Thuhr ("Noon") Prayer: It begins just after the sun's zenith (or "high noon"), as soon as it begins to decline, as the scholars have unanimously agreed.(4) Its time extends until the entrance of 'Asr Prayer, according to the hadeeth, "The (time of) Thuhr is when the sun has begun to decline, until one's shadow is as long as his height, until the entrance of 'Asr time."(5)
'Asr (Afternoon) Prayer: As mentioned clearly in the previous hadeeth, the time of 'Asr Prayer begins at a mid-way point between Thuhr and Maghrib, when a person's shadow is as long as his height.(6) The time of 'Asr extends until sunset. The Prophet (may Allaah raise his rank and grant him peace) said, "Whoever has prayed one rak'ah (unit) of the 'Asr Prayer before sunset has caught the (time of) 'Asr."(7)
Maghrib ("Sunset") Prayer: It begins after the sun has completely set, according to scholarly concensus.(8) Its time extends until the entrance of 'Eshaa' Prayer. The Prophet (may Allaah raise his rank and grant him peace) said, "And the time of Maghrib Prayer extends so long as there is some glow left on the (Western) horizon."(9) This period of time is usually a little over an hour in most places.
'Eshaa' (Evening) Prayer: It begins after the last glow of the sun has left the Western horizon. Its time extends until half of the night. The Prophet (may Allaah raise his rank and grant him peace) said, "And the (time of) 'Eshaa' extends to half the night."(10)
Fajr (Dawn) or Subh Prayer: It begins at the first light of the dawn of the sun, the first glow on the Eastern horizon where the sun will rise from. This is understood from the Verse, "ýUntil the white thread (of the dawn) becomes distinguishable from the black thread."(11) It extends until the sun begins to rise, according to the hadeeth, "And the (time of) Subh Prayer is from the first light of dawn until sunrise."(12) This period of time is usually a little over an hour in most places.
These are the times of the five daily prayers in Islaam, as Jibreel (peace be upon him) taught Muhammad (may Allaah raise his rank and grant him peace). The times of the prayers are all based on the positions of the sun, in a way that makes it easy for the majority of the people on earth to know them without any difficulty whatsoever.
As stated by the Permanent Committee of Scholars for Research and Fatwaa: "The easy way that is in line with the fitrah (the natural state things are created upon) is to rely on the indications in nature (the positions of the sun) that have been indicated in the Islaamic Legislation to determine the times of the prayers."(13)
This excerpt is part of a larger beneficial post "Prayer Schedules: Important Rulings, Guidelines, and Cautions" which can be found at the link directly above. You can find references for the above information there as well as more beneficial information, in shaa Allah.