<b>Aim:</b> Positron emission tomography (PET) imaging is a useful tool for assisting in correct differentiation of tumor progression from reactive changes. O-(2-18F-fluoroethyl)-L-tyrosine (FET)-PET in combination with MRI can add valuable information for clinical decision making. Acquiring FET-PET/MRI simultaneously allows for a one-stop-shop that limits the need for a second sedation or anesthesia as with PET and MRI in sequence. PET/MRI is challenged by lack of a direct measure of photon attenuation. Accepted solutions for attenuation correction (AC) might not be applicable to pediatrics. The aim of this study was to evaluate the use of the subject-specific MR-derived AC method RESOLUTE, modified to a pediatric cohort, against the performance of an MR-AC technique based on deep learning in a pediatric brain tumor cohort. <b>Methods:</b> The modifications to RESOLUTE and the implementation of a deep learning method were performed using 79 pediatric patient examinations. We analyzed the 36 of these with active brain tumor area above 1 mL. We measured background (B), tumor mean and maximal activity (T<sub>MEAN</sub>, T<sub>MAX</sub>), biological tumor volume (BTV), and calculated the clinical metrics T<sub>MEAN</sub>/B and T<sub>MAX</sub>/B. <b>Results:</b> Overall, we found both RESOLUTE and our DeepUTE methodologies to accurately reproduce the CT-AC clinical metrics. Regardless of age, both methods were able to obtain AC maps similar to the CT-AC, albeit with DeepUTE producing the most similar based on both quantitative metrics and visual inspection. In the patient-by-patient analysis DeepUTE was the only technique with all patients inside the predefined acceptable clinical limits. It also had a higher precision with relative %-difference to the reference CT-AC (T<sub>MAX</sub>/B mean: -0.1%, CI: [-0.8%, 0.5%], <i>p</i> = 0.54) compared to RESOLUTE (T<sub>MAX</sub>/B mean: 0.3%, CI: [-0.6%, 1.2%], <i>p</i> = 0.67) and DIXON-AC (T<sub>MAX</sub>/B mean: 5.9%, CI: [4.5%, 7.4%], <i>p</i> < 0.0001). <b>Conclusion:<...