Praise be to Allah.
What is required of the Muslim is to venerate the religion of Allah (may He be exalted) and its symbols.
Allah (may He be exalted) says (interpretation of the meaning):
“That [is so]. And whoever honors the symbols of Allah - indeed, it is from the piety of hearts”
Part of that is venerating and respecting the Prophet (blessings and peace of Allah be upon him) and his Sunnah.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
Whoever believes in the oneness of Allah’s divinity and the message of His slave and Messenger, then does not follow this belief with what it requires of respect and honour, which is something that resides in the heart and is reflected in one’s behaviour and attitude – rather after he claims to believe, he shows disrespect, disregard and scorn in word and deed – then his having this belief is the same as his not having it. That will lead to the corruption and invalidation of that belief, and it will lead to the loss of what it could contain of benefits and a positive impact on his character and behaviour, because belief purifies and rectifies the heart, so when it does not purify and rectify the heart, that is only because it has not taken root in the heart.
End quote from as-Saarim al-Maslool (3/700).
What appears to be the case is that explaining hadiths to the children, then printing them and asking the children to memorize them and colour them in, is not contrary to respecting the Prophet’s Sunnah. The aim is to have the children memorize this hadith and to make that easy for them with some permissible, fun activity that they like, namely colouring and drawing, and similar educational methods that help to achieve the noble aim that is prescribed.
Based on that, there does not seem to us to be anything wrong with the method mentioned in the question.
And Allah knows best.