Just because your child will be playing fun online games doesn't mean the same value won't be there. Create a comfortable study zone. Turn off outside distractions such as cell phones, radios or TVs.
Since 3rd grade math relies on the concepts that were learned during kindergarten, first and second grades, don't be afraid to start your child at a lower level.
There are many good workbooks available for kindergarten children. However with a regular workbook, a child can do each activity or worksheet only once. A good option is to use printable kindergarten worksheets.
When your child is ready, move on to pencil and paper. Build confidence by letting your preschooler trace simple lines and shapes, then proceed to letters. You can eventually teach your child to write his name by letting him trace or copy it daily. If your child needs help remembering how to spell her name, practice with fridge magnets, letter tiles or alphabet blocks.