On Erev Pesach, matzah may not be eaten the entire day. A child who is
old enough to be part of the seder should as well, not be given matzah to
eat on Erev Pesach.
Halachikly, this restriction begins the morning of Erev Pesach, however,
many have a custom not to eat matzah from Rosh Chodesh, and others
from Purim.
The restriction not to eat matzah does not include matzah that is unfit for
the seder. Therefore, "egg matzah" may be eaten on Erev Pesach. (Please
note that for Ashknazim, "egg matzah" is only permitted to be eaten on
Pesach, and Erev Pesach after the sof zman for eating chametz, by cholim
and the elderly.)
Likewise, matzah that is cooked (e.g. kneidlach) may be eaten on Erev
Pesach (for those who eat g'brochts).
However, matzah that tastes as regular seder matzah may not be eaten
(even if one may not use it for the seder). Therefore, non shmurah matzah
and even year-round "chometz matzah" may not be eaten Erev
Pesach. Likewise, g'brochts cake (made from matzah meal) may not be
eaten on Erev Pesach.
All mezonos (e.g. kneidlach) should not be eaten after "Sha'ah Asiris", 4:40
p.m., as this can diminish one's appetite for the seder matzah. Fruits,
vegetables, fish, and meat may be eaten in small quantities.