Praise be to Allah.
Practising sports of various kinds that do not go against the rulings of sharee’ah and that fulfil the aim of worshipping Allah is one of the things that are encouraged by Islam, so as to attain physical strength and mental health. The evidence of the Quran and Sunnah indicates that this is allowed in sharee’ah and is in fact encouraged.
But in some cases these sports may be haram, not in and of themselves, but because they include some haram things. This applies to what you have mentioned in your question.
An example of the haram things that may happen is bowing to someone other than Allah. It was narrated that Anas ibn Maalik (may Allah be pleased with him) said: “A man said, ‘O Messenger of Allah, when one of us meets his friend, can he bow to him?’ The Messenger of Allah (peace and blessings of Allah be upon him) said, ‘No.’ He said, ‘Can he hug him and kiss him?’ He said, ‘No.’ He said, ‘Can he shake hands with him?’ He said, ‘Yes, if he wishes.’” (Narrated by al-Tirmidhi, 2728; he said it is a hasan hadith. Also narrated by Ibn Maajah. 3702. The hadith was classed as hasan by al-Albani in al-Silsilah al-Saheehah, 160).
Ibn Taymiyah said: “With regard to bowing in greeting, this is forbidden as narrated in al-Tirmidhi from the Prophet (peace and blessings of Allah be upon him), that they asked him about a man who meets his brother and bows to him, and he said no to that. That is because it is not permitted to bow or prostrate for anyone except Allah.” (Majmoo’ al-Fatawa, 1/377).
If you know that the person whom you invite to join will do something haram or something that is a kind of shirk, then you should not do that, whether the one whom you invite is a child or an adult, because that is a kind of cooperating in sin, and Allah says (interpretation of the meaning):
“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression” [al-Maa'idah 5:2]
May Allah help us and you to do that which He loves and which pleases Him. May Allah send blessings and peace upon our Prophet Muhammad and his family and companions.