Making my daughters first schoolbag, need advice

hey all, so my daughter is starting kindergarten this year and she asked me to make her a schoolbag. now granted Kindergarten isnt going to neccessitate a bag able to hold books or large amounts of weight, but i'd like to make sure its good and sturdy for her. i was thinking of doing a messenger style bag but more rounded on the corners and i'd like to add a portion of fabric around the bottom and sides so that it could sit flat on the ground. it would be somewhat like the one at this link in design but smaller

http://www.ebags.com/product/ducti/utility-lap-top-bag/110453?productid=1291513

so my question is what would be the best way to reinforce the seams on the bottom and around the straps to withstand a childs wear and tear? i dont have a sewing machine with a serger so thats not an option, but i do have a decent machine. was thinking maybe a doublestitch would work? ANY suggestions appreciated