LB: There is no requirement that the afikoman has to be hidden. The custom for children to “chaap” the afikoman is twofold: 1) so that they should stay awake for the seder.
2)It is related to Yaakov Avinu receiving the brochos instead of Eisav which took place on the day we celebrate Pesach. The passuk says ????????? ???? ??????? ?????????? ????????? ???????????:
The numerical value of ?????????? is 287. Beis =2, mem =40 (x2=80) resh=200 and hay =5. 200+80+5+2=287.
afikoman is also 287 (alef=1, pey=80, yud=10, kuf=100, vav=6, mem-40, nun=50 (1+80+10+100+6+40+50=287).
It does not actually have to be hidden away unless the adults want to look for it.