The Rising Use of Anticoagulants with kids. What are the sports participation considerations?
"The use of oral anticoagulants in children has increased in recent years, parallel with surgical advances for the treatment of univentricular heart, increasing use of prosthetic valves in children and adolescents and rising numbers of children harbouring giant aneurysms following Kawasaki disease. Vitamin K antagonists (VKA, Warfarin and Acenocoumerol) remain the most commonly used oral anticoagulants in children." 
"During the past decade, there has been an increase in the incidence of venous thromboembolism (VTE) in children." 
"The use of anticoagulant drugs in pediatric patients differs from adults, where children require more frequent monitoring.[4,5] Most recommendations regarding drug use in pediatrics are based on extrapolation from adults and in some circumstances such extrapolation may be inappropriate.." 
"Bleeding is the main side-effect. The risk of major bleeding is 0.5% per patient-year." 
"The dose of Warfarin needs to be increased when coadministered with anticonvulsants like phenobarbital and carbamazepine. Other drugs interacting with warfarin include aspirin, steroids, nonsteroidal anti-inflammatory agents, alcohol, fluconazole, metronidazole, amoxicillin, rifampicin, chloramphenicol, sulfamethoxazole–trimethoprim combination, etc. Breast milk-fed infants are more sensitive to warfarin as compared to formula-fed infants due to the lower vitamin K content in breast milk. Warfarin effect may be modified by several food items such as liver, broccoli, Brussels sprouts, spinach, coriander, cabbage and other green leafy vegetables. Patients should be advised to maintain constant dietary habits while on warfarin." 
Side Effects and Emergency Care When Taking Coumadin
Get emergency medical help if you have any of these signs of an allergic reaction to Coumadin: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Coumadin may cause you to bleed more easily, which can be severe or life-threatening. Seek emergency medical attention if you have any unusual bleeding, or bleeding that will not stop. You may also have bleeding on the inside of your body, such as in your stomach or intestines. Call your doctor at once if you have black or bloody stools, or if you cough up blood or vomit that looks like coffee grounds. These could be signs of bleeding in your digestive tract.
Also call your doctor at once if you have:
pain, swelling, hot or cold feeling, skin changes, or discoloration anywhere on your body;
sudden and severe leg or foot pain, foot ulcer, purple toes or fingers;
sudden headache, dizziness, or weakness;
easy bruising, purple or red pinpoint spots under your skin, bleeding from wounds or needle injections;
pale skin, feeling light-headed or short of breath, rapid heart rate, trouble concentrating;
dark urine, jaundice (yellowing of the skin or eyes);
little or no urinating;
numbness or muscle weakness; or
pain in your stomach, back, or sides. 
1 Oral anticoagulants in pediatric cardiac practice: A systematic review of the literature
2 Anticoagulant therapy in pediatrics