Can going from 22.5mg of methotrexate injections to 25mg (in a 6year old) increase your chance of side effects? so if didn't have before can have now?

See details: There is a small increase in risk but almost anyone that tolerates 22.5 mg weekly will also tolerate 25 mg weekly. However, both are relatively high doses for a 6 year old.

Yes, definitely: A weekly dose of 22.5mg of Methotrexate injections is already a pretty high dose for a 6yo child, so i would not go up further. I would reduce it to 12.5 or 15mg of Methotrexate weekly injections and add either Enbrel (etanercept) (less painful) or humira(equally effective and better for eye inflammation and ibd-related arthritis).Talk to your rheumatologist about it.Biologics are very safe with fewer side efx.