Lessons in Good Behaviour for Medieval and Tudor children

'In bed if thou fall harboured to be
With fellow, master or highte degree
Thou shalt enquire by courtesy
In what part of the bed he will lie.
Be honest and lie thou far him from
Thou art not wise but thou do so.'
  The Boke of Curtasye ed, J.O. Halliwell, Percy Soc. Tracts Vol. 4 1849 (c. 1430-40)

This sounds like a delicate warning about sexual molestation which books of manners give no advice on but which was probably a common problem in the promiscuous living conditions of medieval Europe.
Sharing a bed with a stranger was quite normal both in private houses and crowded inns.  The 5th Earl of Northumberland's Gentlemen and Children of the Chapel, for instance, are descriped in the household accounts of Henry VIII as normally sleeping two gentlemen or three children to a bed.
(EETS Vol. 32, Extracts from the Household books of the Earl of Northumberland..c. 1510-11)

Four children of Sir Thomas Lucy III, 1619.  National Trust

Some of the general advice to children in the books of courtesy of the Middle Ages and Tudor times has been popular with parents and teachers from time immemorial, and brings these long ago children vividly to life:

'Child I warn thee in all wise
That thou tell troth and make no lies.....
Child, climb thou not over house nor wall
Forno fruit, birds nor ball
And, child, cast no stones over mens houses
Nor cast stones at no glass windows.
       EETS vol. 32 Symon's lesson of wysdome for all maner chyldren

Several books of courtesy suggest that under fourteens were more mature than most boys that age are now:

And son of one thing I the warn
And on my blessing take good heed
Beware of using of the tavern
And also the dice I thee forbid
And flee all lecherie in will or deed'
  How the wise man taught his son, ca. 430,  EETS vol. 32

'....ye shall nhot you excuse
From breecheles feast (beating) and I may you espy
Playing at any game of Ribaldry
  Caxton, advice to Lytle John ca. 1477-8, ed. F.J. Furnivall, EETS extra series 5, 1868

O Little childe Eschewe thou ever game
For that hath brought many one to shame
As dicing, and carding And such other plays
Which many undoeth as we see nowadays.'
'Tale a Toppe, if though would playe
And not at the hasadrye'
   F.S. Seagar The schoole of vertue...1557 EETS Vol. 32

And be ware and wyse how that thou lokys
Ouer any brynk, well or brokys...
For many chyld without drede
Is dede or dysseyuyd throw ywell hede...
And but thou do thou shat fare the worse
And therto be bete on the bare ers....'
   Symon's lesson of wysdome EETS Vol. 32

As might be expected in a society where the church was very much a part of everyday life, most books of manners impress on children the importance of observing their religious duties.  Symonds in his Lesson of Wysdome says:
  'For make no crying, Japes nor plays
In holy church on holy days.

Symonds also advises, with an eye to the child's future career:
'And lerne as fast as thou may and can
For owre byschope is an old man
And therefor thou most lern fadst
If thou wolt be bysshop when he is past...
  Symon's lesson of wysdome...EETS Vol. 32