Can I take photos or videos of the children at training and matches?

Only within your club's photography policy. NSPCC Sport's guidance:

• Consent: for a child under 16, consent must be obtained from a parent or carer before taking any photos or videos. Children aged 16 or over may give their own consent if they understand what they're agreeing to, though telling parents is good practice. Anyone can withdraw consent at any time, and that must be respected.
• Have a policy: an organisation that uses or shares images of children must have a policy covering how images are used online and in print, how they're stored, and how children are kept safe. Share it with parents, carers and spectators before events.
• Names: don't publish children's names or other personal details with their images (except where necessary, for example promoting elite young athletes). Be cautious about tagging children on social media.
• Spectators: ask parents and spectators not to share images online, because other people's children can be identified from them.
• Changing rooms: no phones or camera devices in changing or shower areas, for anyone: participants, spectators, staff and volunteers.
• Livestreaming: tell families in advance and get consent, use wide general shots rather than close-ups, and make sure the stream isn't recorded.